Airborne renewable energy generation and storage

ABSTRACT

An energy collection system uses one or more airborne energy collection vehicles having a lighter-than-air balloon structure. The balloon structure has an outer gas envelope formed of a substantially inelastic material and an inner gas envelope at least partially separate from the outer gas envelope, contained within the outer gas envelope and separated from the outer gas envelope by a flexible diaphragm. The space between the outer and inner gas envelopes is filled with air. An air chamber pressurization mechanism maintains the outer gas envelope gas pressure at a target value. An energy storage facility receives energy from a photovoltaic collector array and converts the received energy to stored energy. Storage of the received energy can be accomplished by conversion of a precursor to a high energy fuel as the stored energy, by use of storage batteries or by storage in an inertial mass.

BACKGROUND Field

The present disclosure relates to the field of renewable energyproduction. More specifically, the disclosed technology relates to anautonomous unmanned aircraft system coupled with a solar energycollection element, an electricity generation element and anelectro-chemical cell, which is intended to capture solar energy ataltitude.

Background

The demand for renewable sources of energy is expanding rapidly as wegain understanding of the impacts of fossil fuels. Of the varioussources of renewable energy available, solar power generation may havethe greatest potential but as yet has been held to a fraction of globalpower supply. This is due primarily to several limitations in itstraditional modes of implementation. These limitations include the costof installation, unreliability of the power supply, and non-uniformaccessibility to solar energy. More specifically, a traditional solarinstallation's output will vary dramatically depending weather, season,location and time of day—including the obvious situation that no energyis produced at night. Some geographical areas are less suitable thanothers due to overall weather patterns or being further from theequator. Currently, these issues are mitigated through paring solarinstallations with fossil fuel back-up generators or through batterystorage. These additional requirements greatly increase the cost ofsolar installations while still failing to free solar energy fromgeographical constraints.

The disclosed technology is an “aerosolar” energy harvesting system,capable of harvesting solar energy from an airborne platform. Anaerosolar energy harvesting system shifts the location of solar energycapture to a lighter-than-air Unmanned Aerial Vehicle (UAV) and includesan onboard electro-chemical cell so that energy can be stored to bedistributed later and used where and when it is needed. This providesseveral benefits. First, the placement of solar energy collectors on anaerial platform allows the conversion to be used at high altitude, suchas in the tropopause, an elevation with predictable and reliablesunlight exposure at several times greater yearly insolation than atground level regardless of geographic location. Second, the storage ofgenerated electricity in batteries allows the stored energy to be usedat whatever time it is needed, eliminating the need for other costlystorage or backup power plant installations. Third, if the system isused to produce hydrogen, the storage medium of hydrogen gas can bemarketed directly to the hydrogen fuel economy or (along with the oxygenalso produced as part of the electrolysis process), and sold as a highpurity gas for medical or research purposes.

SUMMARY

An energy generating system uses an airborne energy collection vehiclehaving a balloon structure. The balloon structure has a lighter than airenvelope structure with an outer gas envelope formed of a substantiallyinelastic material and at least one inner gas envelope at leastpartially separate from the outer gas envelope. The inner gas envelopeis at least partially contained within the outer gas envelope, and isconfigured to hold lifting gas as a buoyancy medium, with at least aportion of a space between the inner gas envelope and outer gas envelopefilled with air. A flexible diaphragm forms at least a portion of theinner gas envelope separate from the outer gas envelope and is containedwithin the outer gas envelope. The flexible diaphragm causes the innergas envelope to maintain an equilibrium pressure with the outer gasenvelope and allows expansion and contraction of the inner gas envelopeto substantially fill the space of the outer gas envelope from arelatively smaller fraction of the outer gas envelope. An air chamberpressurization mechanism is provided, which is capable of maintainingthe outer gas envelope gas pressure at a target value. An air chamberpressurization controller monitors the outer gas envelope pressure andeither pumps in air or vents air to bring a gauge pressure to the targetvalue.

A photovoltaic collector array receives solar energy and an energystorage facility receives energy from the photovoltaic collector arrayand converts the energy to stored energy. In one configuration, theenergy storage is accomplished by converting a precursor to a highenergy fuel. In another configuration, energy storage is provided bystorage batteries. In another configuration, energy storage is providedby one or more inertial masses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are schematic diagrams showing side views (FIGS. 1A and 1B)and end views (FIGS. 1C-1E) of an airborne floating solar energyfacility.

FIG. 2 is a configuration in which a balloon section uses a diaphragm toestablish a separate lift gas chamber and air chamber.

FIG. 3 is a schematic diagram showing a lift control system.

FIGS. 4A-4C are schematic diagrams of the balloon-to-externally carriedsection tethers, showing half of the system (FIG. 4A), the tethers alone(FIG. 4B), and according to changes in the balloon orientation, as isshown in (FIG. 4C).

FIGS. 5A-5C are a series of schematic diagrams depicting the airbornefloating solar energy facility in side view, tracking the sunlight fromthe horizon to vertical by changing the angle of the balloon.

FIGS. 6A and 6B are schematic diagrams showing a wing seen from thefront of the platform, unfurled and being used for steering (FIG. 6A),and the wing pulled in tight and cinched down (FIG. 6B).

FIG. 7 is a diagram showing the use of battery energy storage

FIG. 8 is a schematic diagram showing the floating solar energy facilitylanding, automated capture, refueling and release.

FIG. 9 is a schematic diagram showing the control of the airbornefloating solar energy facility.

DETAILED DESCRIPTION

Overview

The aerosolar energy harvesting system taps into a renewable sourcewhich has the critical qualities needed for next generation global powersupply—namely, the aerosolar energy harvesting system is safe, scalable,clean, accessible, affordable, and stable. The proposed system is safebecause it uses only easily controllable photovoltaic systems. It isscalable and clean because production increases with a number ofairborne floating solar energy facilities and draws on solar energy,which is the most plentiful source of power. The aerosolar energyharvesting system is accessible because the tropopause is available fromany point on the planet. It is affordable because the solar powerdensities in the tropopause run significantly higher than for groundedsystems, and stable because the capture generally occurs above theweather of the lower atmosphere, so it is a reliable daily resource.

The airborne floating solar energy facility is an autonomous mobileplatform coupled with a solar energy collection element and anelectro-chemical cell. In one non-limiting example, the electro-chemicalcell stores energy by drawing in low-energy precursor chemical(s),adding energy via a chemical reaction, and storing the resulting fueland possibly oxidizer (later referred to as part of the “fuel”)chemical(s) as a form of chemical potential energy as a high energyfuel. For purposes of this description, a “high energy fuel” referencesa fuel with substantial chemical energy density, such as hydrogen orhydrogen and oxygen. Hydrogen has a specific energy value of 142 MJ/kg,which contrasts with methane at 55 MJ/kg, diesel fuel at 45-50 MJ/kg andmethanol at 20 MJ/kg. For purposes of this description, a fuel with aspecific energy value of at least 10 MJ/kg would be “high energy”because it is effective for storage of energy. High energy fuels havinga specific energy value of at least 25 MJ/kg are desirable, and highenergy fuels having a specific energy value of at least 90 MJ/kg aremore desirable.

While oxygen is chemically not a fuel, purified oxygen can be used toenhance energy production, and for the purposes of storing energy,oxygen is described as part of a fuel payload because it has an energyproducing value.

In another non-limiting example, called the “battery approach”, theelectro-chemical cell is a battery system, such as a lithium-ion batterysystem.

One non-limiting example mode for a solar to chemical energy conversionsystem is a photovoltaic collector array driving the electrolysis ofwater. The solar collector is mounted to an inflated balloon where itconverts sunlight to usable energy. In one non-limiting example mode,called the “hydrogen approach”, the solar panel electricity is used topower an electrolysis unit producing hydrogen and oxygen. The hydrogenand oxygen are stored in attached tanks and in the balloon envelopeitself. Thus, according to the hydrogen approach, not only is thehydrogen the end product, but it also can be the lifting gas used tokeep the system afloat.

The unmanned airborne floating solar energy facility is intended to beone of a group or school of airborne energy collection vehicles, whichfunction as airborne floating energy facilities. The airborne floatingenergy facilities are solar energy facilities within close proximity toeach other and working with at least one landing/loading station. Thislanding/loading station may be on the ground, may be aloft, or may beafloat on a ground-based vehicle such as a ship. In the hydrogenapproach, an airborne floating solar energy facility takes off from thestation with a full load of water, and ascends above the clouds into thetropopause region. The airborne floating solar energy facility residesin the tropopause region until it has collected enough energy to largelyconvert their supply of precursor to fuel, which in the example version,is a conversion of the water supply to hydrogen. Once the conversion iscomplete, the solar energy facility descends back to the ground stationwhere the energy stored in the airborne floating solar energy facilityis offloaded, via either transfer of the fuel or via chemical reaction,and the precursor supply is replenished. In this example version, thismeans offloading the generated hydrogen and oxygen; then refilling withwater. The solar energy facility then re-launches, repeating the cycleendlessly, except for maintenance. The solar energy facilities will thussupply a consistent supply of energy to the station, scaling with thenumber of solar energy facilities.

In the battery approach, the solar energy facility takes off with a loadof substantially discharged batteries. The batteries are charged whilethe facility is airborne and the facility descends back to the groundstation to discharge the batteries to deliver the captures and storedelectricity to a customer of the electrical grid, with conversion of theelectricity to alternating current as required.

Floating Solar Energy Facility Components

FIGS. 1A-1E are schematic diagrams showing side views (FIGS. 1A and 1B)and end views (FIGS. 1C-1E) of an airborne floating solar energyfacility 100. In overview, the airborne floating solar energy facility100 comprises balloon section 101 or balloon structure, and externallycarried section, described as a keel 102. Keel 102 is attached toballoon section 101 by tethers, including main keel tether 105.

The balloon section 101 comprises outer envelope 121, within which ispositioned inner envelope 123. Inner envelope 123 forms lift gas chamber125, which contains a lift gas such as, by way of non-limiting example,hydrogen. The space between inner envelope 123 and outer envelope 121 isair chamber 127, which is pressurized to establish balloon section 101as a superpressure balloon.

Balloon section 101 also supports solar panels 131, which, by way ofnon-limiting example, are mounted on an exterior of outer envelope 121.

Keel 102 supports component which are external to balloon section 101,which may comprise fuel storage components. In the example of use of abattery for storage of energy, the battery may be located in keel 102.

In the example of the production of high energy fuel, keel 102 may carrywater tank 141 which carried a precursor (water), hydrogen storage tank142 and oxygen storage tank 143. Electrolysis unit 147 may also belocated in keel 102 and receive energy from solar panels 131.

Also provided on airborne floating solar energy facility 100 is wing151, which is depicted in FIG. 1A in a partially retracted state, and inFIG. 1B in an unfurled state, controlled by wing bearing 153 mounted onmain keel tether 105.

Inner envelope encloses a lift gas chamber. Between the interior and theexterior envelope is the air chamber. Two sets of thrusters 161, 163 areattached to the inflated balloon 101, with set 161 able to generatethrust in the X-axis and set 163 able to generate thrust in the Y-axis.X-axis thrusters 161 are anchored in place by attachment to compressionbar 165, which has one end held in location by vertical tension cables167 and horizontal tension cables 168. This compression bar also acts asa rotary axis for X-axis thrusters 161, which are forced to anorientation by the vertical tension line running down to the keel 102.This line forms a Y shape 171 with a main cable that splits into twoarms below X-axis thrusters 161. These two arms attach to either end ofthe horizontal lever arm on X-axis thrusters 161. The bottom of the Y171 contains a compliant element to account for length changes. The keelmass is held by main keel tether 105 which branches out at is approachesthe balloon equator. Each branch point uses a small bearing to allow forreadjustment of the tension direction on the branching network.

Wing is attached to the main keel tether via a bearing, and controlledvia lines driven by motors on the keel payload. The keel payloadcontains, in the hydrogen energy storage instantiation, a water tank, anelectrolysis unit, a hydrogen tank and an oxygen tank.

The balloon is formed in an ellipsoid shape, symmetric around the Y-Zplane to provide equivalent drag whether the wind is flowing in the +xor −x axis direction. This ellipsoid shape includes the long axis(X-axis) being longer than the Y- and Z-axes, which is intended tominimize drag for flows that occurs around a sphere, allowing the giventhrust force to produce higher relative travel velocity during landing,and resist higher wind gusts during geostationary operation.

As can be seen between FIGS. 1D and 1E, expansion of air chamber 127results in contraction of lift gas chamber 125. This establishes a“reverse ballonet” configuration, in which the lift gas is in theinterior envelope 123.

The exterior balloon skin of outer envelope 121 should be able to handleultraviolet (UV) radiation, low temperatures and moderate continuousstress, while resisting significant gas diffusion. The presentlyenvisioned skin is a metalized polymer, high strength fabric laminate.In one version, the balloon skin is protected by an aluminization layer.The aluminization layer is a few 10's of nm thick aluminum filmdeposited on an approximately 10 μm Biaxially-oriented polyethyleneterephthalate (BoPET) layer. The aluminum layer reduces the balloon'sgas permeability. The metallized balloon skin is attached to a highstrength fabric such as a Kuraray Vectran™, Kevlar®, or carbon fiberweave, which is sized to ensure a significant (>10×) safety factor. Themetallized base layer may be coated while the high strength fabric isunder strain (thermal or mechanical) to ensure the film is slightlycompressively preloaded. The compressive preload should be tuned tolargely cancel the balloon gauge overpressure induced stress. Across-layered load layer composed of thin strands like a window screenwill act to halt tear formation in the gas blocking layer. An additionalthin, and easily replaceable, UV resistant layer such asmetallized-face-out-Mylar® or polyethylene terephthalate (PET) may beplaced over the sunward facing part of the balloon (on top of the loadlayer, connected at certain mounting points) to act as a sunblock andreduce balloon skin damage.

Inner envelope 123 is protected from external damage by outer envelope121. Inner envelope 123 is designed to efficiently contain lift gas, butis flexible enough to contain the lift gas with little pressuredifferential between lift gas chamber 125 and air chamber 127.

FIG. 2 is a configuration in which balloon section 201 uses outerenvelope 221 and diaphragm 223 to establish separate lift gas chamber225 and air chamber 227. Diaphragm 223 is a highly flexible diaphragmwhich separates the overall shape into two distinct chambers orenvelopes 225, 227, an outer envelope and an inner envelope. Diaphragm223 may be either elastic or non-elastic, however non-elastic ispreferred. Diaphragm 223 should include extra material so it can bedeformed to change the relative chamber sizes of outer envelope (airchamber) 227 and inner envelope (lift chamber) 225. The non-elasticnature of diaphragm 223 is considered for two reasons. First, the lowstrain cycling during operation reduces the damage to the diaphragmmaterial; second it helps to effectively pass pressures between the twochambers 225, 227, so they are always nearly equal in pressure. One sideof the diaphragm is filled with lift gas, which is hydrogen in onenon-limiting example configuration, but could also be otherlighter-than-air gases and mixtures such as helium, ammonia or ahydrogen and helium mixture. The other side of diaphragm 223 is filledwith ambient atmospheric gas (air). In a non-limiting example, diaphragm223 is able to allow the lift chamber 225 to occupy from about 5% up toabout 95% of the total balloon volume. In the example, the structure ofdiaphragm 223 is that of a separate balloon within the main volume, suchthat the hydrogen containing chamber 225 is not in direct contact withthe exterior of the balloon 201 at nearly any point. This ensures thatthe lift gas, a flammable gas in this instantiation, is separated fromignition or puncturing objects by an insulating layer of air. Any tearsin the exterior balloon would then force the venting of air rather thanvaluable lift gas. Additionally, any contact with an external flamesource would not ignite the hydrogen, but would rather only cause theexterior surface to char.

The construction is roughly that of a reverse ballonet configuration, asthe primary lifting gas is held in the inner envelope and air or asecondary gas held in the outer envelope (between the inner and outerenvelopes). The result is that the inner envelope is used to maintain asealed environment to prevent lift-gas loss, whereas structuralintegrity and ultraviolet light resistance is provided by the outerenvelope.

While a two envelope configuration is described, it is also possible toprovide additional envelopes as convenient, such as for providing asecondary lifting gas that is expected to remain contained within theairborne floating solar energy facility at all times during flight, orfor more layers of containment around the lift gas envelope. One exampleof extra layers of containment would be a design with (referring toFIGS. 1A and 1B) inner lift gas envelope 123, then a second “backup”envelope (not separately shown) around inner lift gas envelope 123. Thespace between these two envelopes could be filled with an inert liftgas, such as helium. Finally, these two envelopes would be placed withinthe exterior balloon envelope. The dual inner envelope design wouldprovide a cushioning layer of inflammable gas that still provides liftbut would not ignite. The gas in the “backup” envelope could be sensedfor the interior lift gas—hydrogen in the example—as well as air.Likewise the air envelope could be sensed for hydrogen and helium.Finally, the innermost inner hydrogen envelope could be sensed forhelium. Detection of these gases would determine where a tear hadoccurred, yet due to the intervening inert gas, such a tear would notimmediately result in a flammable gas mixture. This would provide thesystem time to return to ground for repairs before the gas mixturebecame dangerous. The air blower can be used to blow air into the airchamber if a hydrogen leak is detected. The air flow will act todisperse the hydrogen so it is kept below the flammable threshold (4% byvolume). The air and hydrogen mixture can be drawn out of the airenvelope either by one of the air blowers running in reverse, or specialvents located around the balloon. These special vents could be locatedat the top of the air envelope to help selectively vent thelighter-than-air gas.

Placing the lifting gas in the inner chamber 125, 225 reduces the chanceof a puncture that drains all the lift capability from the balloon, orthe ignition of the lift gas. This also simplifies the fabrication ofthe balloon, as two separate structures. The balloon fabric design isalso decoupled, as the exterior fabric does not have to have nearly ashigh quality impermeability since it only keeps in pressurized air.Likewise, the interior balloon fabric is not operating with anysignificant skin stresses, so does not require nearly the samereinforcement layer as the exterior skin. Since the external surface ofthe balloon is the outer chamber, ultraviolet exposure is encountered bythe outer enclosure, which is also protected by the aluminization. Theinner envelope is designed to be gas impermeable and relies on theexternal metallized skin to provide UV protection. The reverse ballonetconfiguration also has advantages in terms of safety, in that the liftgas, if flammable, is not as exposed to external damage as would be thecase if the hydrogen were contained by the outer envelope.

The outer gas envelope is made of reinforced material which issubstantially inelastic. Significantly, the outer gas envelope isconstructed to be highly resistant to ultraviolet energy, such as isexperienced in the tropopause. Ultraviolet protection can be achieved bythe material being inherently ultraviolet resistant, by aluminization orother protective coating, or by being covered by other components suchas a replaceable UV Mylar film cover, or the photovoltaic collectorarrays, at least where the photovoltaic collector arrays are located.The outer gas envelope may be designed to be ultraviolet opaque, so asto protect the inner gas envelope from the effects of ultravioletradiation.

The use of the reverse ballonet design results in placing the lift gasin the inner envelope. Placing the lift gas in inner lift gas envelope123 provides various advantages which have previously been described andare repeated here in list form for completeness, including:

-   -   1) A reduction in surface area of the lift gas volume, so a        reduced likelihood of lift gas loss through tears. There is only        one balloon surface (inner), as opposed to two (inner and outer)        that contains the lifting gas.    -   2) A decoupling of the outer balloon skin functions. In a        conventional design the outer balloon skin is both a gas        containment and a tensile load layer. In the dual chamber        design, limited failure of the gas containment is acceptable, as        a limited tear in the outer skin results only in the loss of air        pressure; not valuable lift gas. This is a significantly more        recoverable scenario, and one that the operator can expect to        encounter when undergoing rapid sustained cycling.    -   3) A decoupling of the gas containment layer. In a conventional        design both the interior and exterior balloon must contain the        lift gas, so a material must be found that retains low        permeability under harsh conditions—UV and tensile loading. In        the disclosed design, the low permeability layer is largely        decoupled from these two other conditions, so the material        design can be much simpler. This is expected to increase the        lifetime of the airborne floating solar energy facility and        reduce the leakage rates of lift gas.    -   4) The reverse ballonet design provides an additional skin layer        between external structures and the lift gas balloon, acting in        a limited fashion to guard the inner envelope, holding the        primary lift gas, from puncture.    -   5) The increased surface area between the air chamber and the        exterior helps achieve both rapid thermal equilibration (needed        for rapid rise/fall) and helps to provide multiple means for to        exchange air. Based on the design topology, a single access        point at the bottom of the balloon such as would be found with        conventional ballonet designs would hinder the air transfer        capabilities.

While inner and outer chambers are described, it is possible to combinea portion of the inner and outer chambers, so that at portions of theballoon, the inner and outer envelope materials are combined. In onenon-limiting configuration, the combination of the inner and outermaterials occurs at the bottom of the balloon, whereas a separate airchamber exists at the top of the balloon, separating the inner and outerenvelope. This point of combination in the inner and outer chambers isan ideal location to pass through tubing and other connections from theexterior of the balloon to the lift chamber.

The center of lift is similarly located to the conventional ballonetdesign. The interior lift gas balloon is able to fill the entire volume,so it does not impede the lift gas from settling against the top of theballoon at low altitudes, the same as the conventional ballonet design.This places the center of lift well above the center of the balloon. Theexternally carried section carried by the balloon will further shift thecenter of mass downwards, so static stability issues are notanticipated.

Control of Lift

While hydrogen is described as both the lifting gas and the high energyfuel, it is also possible to use other gasses such as He, ammonia,hydrogen/helium mixtures, etc., as lighter than air lifting gasses. Thiscan be particularly useful if the other gas is expected to be retainedin the balloon after transfer of the high energy fuel, or is otherwiseused in the handling of the high energy fuel or the low-energyprecursor. Such an alternative lifting gas can be retained either withinthe inner envelope, or within the outer envelope separate from the gasin the inner envelope. To that end, the alternative lifting gas may bekept sealed off from other gases within the balloon with flexiblediaphragms or by other means. The alternative lifting gas may be mixedwith other gases if it is easily separated from the produced fuel, or isacceptable as a component of the produced fuel.

FIG. 3 is a schematic diagram showing a lift control system. Depicted isballoon section 101 with outer and inner envelopes 121, 123, forminglift gas chamber 125, and air chamber 127. Also depicted are precursorsupply tank 141, hydrogen storage tank 142, oxygen storage tank 143 andelectrolysis unit 147, which are located in keel 102 (FIGS. 1A-1E).Superpressure pump 351 provides air to air chamber 127. Lift gas isoptionally pumped from lift gas chamber 125 to hydrogen storage tank142. The lift gas is admitted to lift gas chamber 125 from hydrogenstorage tank 142 by means of valve 255. In addition, in the “hydrogenapproach”, electrolysis/fuel cell unit 147 generates hydrogen and oxygenwhich are stored in tanks 142 and 143 and extracts energy from thehydrogen and oxygen as required.

The lift control system is fundamentally a dual parameter decoupledcontrol of both buoyancy and balloon pressure. For most of the droneoperation, it is less energy intensive to operate the system like thesimpler and more common single parameter control of the balloon pressurewhere buoyancy and pressure are linked. This single parameter mode is asubset of the dual parameter mode that can be engaged by halting themodulation of the lift gas mass. The single mode control only works wellin limited conditions, which are easily exceeded in emergencies. Thedual control framework provides the unique opportunity to switch to themore complex mode in certain cases, such as these emergencies, toprovide an additional layer of redundancy.

Dual parameter decoupled control means the operation of two parallelcontrol loops, one for buoyancy or lift force, and one for balloonpressure. The buoyancy control loop holds the net buoyant force on thewhole blimp to a commanded value by adding or removing lift gas massfrom the lift gas chamber. The balloon pressure control loop holds theballoon pressure to a commanded value of slightly positive gaugepressure by using an air blower and vent system to either add or removeair mass from the air chamber. Both of the control loops, lift andpressure, must be running for the system to operate in a decoupled mode.

The lift gas can be controlled with either an “open cycle” or a “closedcycle” which differ by whether the gas is retained or vented to theatmosphere once removed from the lift gas chamber. Both cycle typesallow the lift gas mass to be controlled in the same manner, the onlydifference is whether power (open cycle) or mass (closed cycle) isconsumed by the cycle. In the “closed cycle” design, vents allow liftgas from a compressed storage tank into the main lift gas chamber, whilethe system uses a compressor to pull the excess lift gas from the liftgas chamber and compress it back into the storage tank on the blimp. Inthe “open cycle” design, extra lift gas can be vented from compressedtanks on the blimp into the lift gas chamber to add lift gas mass andthus increase the buoyancy. Or the lift gas can be vented to theenvironment to reduce buoyancy.

“Single parameter coupled control” means the operation of a singlecontrol loop for buoyancy or lift force in which balloon pressure andlift force change in a coupled manner. This is the mode that occurs ifthe lift gas controller is turned off. Then the balloon pressure and netlift force are directly coupled. For instance, increasing the balloonpressure by adding air mass increases the net mass of the blimp whichreduces the lift force. The preferred mode for lift control in thesingle parameter coupled control scenario is the use of an air blowerand vents to add or remove air from the air chamber. This will act toadd or remove mass from the balloon, considered as a roughly constantvolume container. By blowing air into the balloon, the net massincreases and the pressure rises. The load layer in the skin of theballoon resists significant expansion, so the increase in masssubstantially outweighs the increase in buoyancy due to any volumeexpansion. The balloon is kept at a slight positive gauge pressure, sothat it is fully inflated at all times. The lift control acts byaltering the scale of this gauge pressure. An increase in the gaugepressure due to added air will cause the system to fall. A decrease inthe gauge pressure due to removed air will cause the system to rise. Theair blower is controlled to maintain a target pressure in the airchamber, as the pressure is related to the net lift. A Non-limitingexample of the base gauge pressure is 1 kPa with upper and lowerpressure bounds of 0.5 to 1.5 kPa.

Most of the time, the balloon lift control system will run as a singleparameter coupled control of lift and pressure. The lift gas chamber cangenerally be left at a set mass in non-emergency situations to provide aconstant buoyant balance to the whole system, then the variable liftforces can be generated by modulating the pressurize in the air chamber.The single coupled control operate is simpler and less energy intensivethan the dual decoupled control because of the pressure differential andthe gas density. The pressure differential determines the difficulty ofmoving the gas from the low to the high pressure side, and thisdifferential is only about 1 kPa for the air in the preferred mode, butcan be upwards of 20 bar (2 MPa) in the preferred mode for the lift gasto bring it back into the compressed gas tank. Thus much more energy isrequired to move a given volume in the lift gas case. Second, the airdensity is always much higher than the lift gas, so gas transfer systemslike blowers and compressors will be more effective at transferring massby moving air around than moving lift gas.

The limit of the single parameter coupled control is when the situationdeviates outside of normal conditions. In these cases, it may benecessary to independently control lift and balloon pressure. Becausethese conditions are the extreme circumstances, and thus the lift gasmass control will only rarely be used, the “open cycle” design ispreferred for the lift gas controller to save on cost and mass. Forinstance, if the balloon exterior develops a tear, and can no longermaintain significant gauge pressure, then the single parameter coupledcontroller cannot bring the balloon on down. Or in high wind scenarioswhere the balloon pressure must be increased to maintain rigidity. Inthese cases, the lift control system can be shifted to the dualdecoupled parameter mode where the lift gas mass is now being activelycontrolled.

The dual decoupled control system allows for control of the liftprovided by the balloon based on the fact that hydrogen at nearlyambient pressures will generate a nearly constant lift force that is amultiple of its weight, regardless of the exterior pressure. This valueis approximately 13× if the hydrogen is exactly at ambient pressure, butfalls slightly to around 12× if the hydrogen is at 1 kPa gauge in thetropopause (due to a slight increase in the hydrogen density atincreased pressure). This reduction in the buoyant force is due to thefact that the atmosphere pressure is around 5 kPa in the tropopause, butthe hydrogen in the balloon is at 1 kPa higher (6 kPa) to ensure theballoon is rigidly inflated. The increase in pressure of the hydrogenraises its density slightly, lowering the resulting buoyant force pervolume. Thus, lift gas mass roughly translates to lift force independentof altitude, assuming that the balloon gauge pressure is held constant.Extra lift gas is stored and supplied from a compressed tank. The airside of the balloon is used to control the pressure in the balloon. Thispressure is passed to the lift gas chamber through the flexiblediaphragm, and throughout the whole balloon.

Such a dual controlled system is a significant advantage insurvivability and control over conventional single control systems, inthe manner used for superpressure balloons. The dual control designenables independent control of the stress on the balloon skin as well ascontrol of the lift force. The controlled interior pressure acts torigidify the structure via pressure rather than material strength. Thisprovides substantial weight and cost savings. Single coupled controllershave these linked, and thus suffer from changing rigidity and shape ifthey have to significantly change the buoyant force. While this worksfine for small deviations (normal conditions), when extreme conditionsare encountered, the single coupled controller systems are less robust.The dual control design guarantees the inflated structure remains at asafe and controlled inflation pressure during all operation, allowing itto be used as a consistently inflated body structure on which thrustersand solar panels may be mounted. This allows heavy, rigid interiorstructural elements to be replaced with reliable inflated structuresthat are much simpler, cheaper, and lighter.

The dual controlled system provides advantages of a fixed size for theoverall balloon envelope, while allowing operation of the lifting gasenvelope as a zero pressure, or near-zero pressure balloon. Theconfiguration also allows the use of an expandable lifting gas envelopethat operates without the use of an elastically expandable skin.Instead, the expansion and contraction of the lifting gas envelope isaccommodated by change of shape of an inner envelope within the confinesof an outer envelope.

The decoupled operation also provides several safety and operationalbenefits, which are important differentiators. These include, 1)allowing for continued transfer of lift gas into the balloon in the caseof an inner lift-gas balloon leak, should the balloon need to maintainlift while trying to return to the station, 2) allowing for altitudecontrol in the possible case of the outer air balloon leak, which for asingle control balloon would result in loss of superpressure controlwhich would mean the balloon could not built up any net weight to createa negative buoyancy required to descend in altitude, 3) allowing for theballoon net lift to be significantly raised, as in the case of attachingto another balloon and attempting to bring that down safely, 4) allowingthe balloon net lift to be significantly lowered, as in the case oflosing components or water payload, where such lift reduction is neededto bring the system home, 5) the load applied to the balloon skin can becontained within a small pressure range during the operation, so thesafety factor is likewise nearly constant, 6) the gauge pressure can becontrollably altered if needed during high winds or other unusualcircumstances to rigidify the balloon, or to reduce pressure in the caseof a known leak, and 7) the lift force can be altered over a greaterscale of net lift than pressure control only. For all of these reasons,the decoupled operation provides substantially more control and safetyto the system. It should be noted that these extra benefits are mainlyemergency circumstances, so the “open cycle” design is considered to besufficient.

The air chamber pressure controller is particularly useful when theballoon is changing altitude, as the air should be rapidly pumpedin/vented to maintain constant gauge pressure. Gauge pressure is theparameter of interest for determining the stress in the balloon fabric.The absolute atmospheric pressure is rapidly changing with the altitudeand so too is the lift gas density. In conventional overpressureballoons, the balloon fabric stress will rise with altitude as the gaugepressure continues to build. This means the balloon fabric must besignificantly overdesigned for most operational conditions. In theproposed design, the air chamber controller will simply vent air to holdto the balloon at a roughly constant gauge pressure and allow the liftgas to occupy an ever greater fraction of the total balloon volume untilthe balloon reaches operational altitude. The reverse occurs when theballoon descends. Lift gas is pumped back into the tank to reducebuoyancy, and the air chamber controller compensates by pumping in moreair to maintain the gauge pressure. The net effect is that more air ispulled into the constant volume of the balloon, increasing its mass whenconsidered as a control volume. The balloon buoyancy drops, generallycausing the balloon to sink. The lift gas volume will fall as theabsolute environmental pressure rises. The air chamber pressurecontroller pumps air into the air chamber to maintain the gaugepressure, counteracting the reduction in lift gas volume. At groundlevel, the balloon will be mostly (>90%) air for a tropopause capablesystem. The lift force does not substantially change during thisoperation for a given amount of hydrogen in the balloon, nor will thegauge pressure that the balloon skin must resist.

The lift gas control will generally be a slower, more power demandingoperation than air chamber pressure control. In essence, the airpressure system provides the immediate change in buoyant force; then isslowly switched out for buoyant force generated by a changed amount oflift gas mass so that the balloon pressure can be brought back to theinitial baseline value. In the dual parameter decoupled control mode,the slow response of the lift gas control system could be aided byhaving the air pressure controller immediately start driving air in/outto generate a lift force change as well as a pressure change. Thispressure change would be held within the upper and lower pressure boundsdetermined by material safety criteria. The air pressure controllerwould now have generated a rapid lift force change. The lift gas masscontroller would be running through this time, slowly adding/removinglift gas mass. As the slower lift gas mass change continues to build,the air pressure controller can begin to bring the balloon pressure backto the baseline term, ensuring that the net buoyant force is held to aconstant value.

This allows the controller to respond much faster by using the pressuremodulation control as the rapid response, but using the hydrogen mass asthe slower, larger scale response. The upper and lower bounds on thepressure command ensure no damage is done to the material by the highfrequency pressure variation.

Balloon-to-Keel Tethers

The balloon is attached to a payload, referred to as the keel, via a setof tethers which allow the balloon (the balloon envelope) to rotate.FIGS. 4A-4C are schematic diagrams of the balloon-to-externally carriedsection tethers, showing half of the system (FIG. 4A), the tethers alone(FIG. 4B), with a focus on one tether line joint. The main tetherbranches out as it rises from the keel, splitting into many smallertethers in order to main contact at many points on the balloon. Thisstructure needs to be able to adapt to changes in the balloonorientation, as is shown in (FIG. 4C). The diagrams show the effect ofthe pulleys on reordering the shape of the tether branching mesh,without reordering the topology of the branching mesh. The topology isthat of a Y-branch at each intersection, with a main tension linesplitting into two lines when following the tether from the keel to theballoon. This structure is maintained, but the relative length of thetwo arms of the Y at each branch (the shape) changes depending on theballoon orientation.

The balloon is attached to the keel via tethers, which can form abranching pattern. There are two main cables which hang below theballoon and attach at the front and rear of the long axis of theelliptical balloon, on their respective side, forming a branchingpattern at each end. The branching pattern is formed not with knots atthe joints but with pulley-like bearings, so the system can adapt todifferent load angles as the balloon changes pointing direction, asshown in FIG. 4C. Additionally, the use of movable joints permits theouter envelope to distort without being stressed by the tethers.

The tethers may, by way of non-limiting example, be wrapped fully aroundthe pulley, producing a 360°+ contact line, as this would avoid issueswith the cables falling off the pulleys should the tension be releasedat any point. The two main cables are largely parallel. They both passthrough a movable cable clamp on the keel, which allows the keel to movealong the main cables. This is presently envisioned as a capstan effectdesign, where the cable is wrapped around a rotational axle, which canbe rotated to move the externally carried section along the line. Thusas seen from above (down the y axis), the cables form an approximate Xwith the keel at the intersection.

Another tether may, by way of non-limiting example, connect thex-direction thrusters to the keel, pointing approximately down at alltimes as the keel will always hang directly below the balloon. FIGS.5A-5C are a series of schematic diagrams depicting the airborne floatingsolar energy facility in side view, tracking the sunlight from thehorizon to vertical by changing the angle of the balloon. After noon thesun starts to set, and the solar energy facility flips 180° in θ-z, andagain uses the angle change to track to the opposite horizon, as will beexplained with respect to solar energy capture.

These x-direction thrusters are on one-axis gimbals, so they can stayhorizontal even when the balloon rotates around the y-axis as shown inFIGS. 5A-5C. The vertical tether connected to the x-direction thrustersis best designed as a Y, connecting to the thruster at two locations,and these two lines meeting some distance down below the thruster. Thisgenerates a strong moment on the thruster to level it. It also allowsvertical tension lines to be placed from the thruster compression barstraight down, passing through the arms of the Y. The balloon is able tochange its angle; however, this tether is always vertical owing to thetank location being held by gravity to be downward. This tether may bemade slightly elastic via the addition of a stretchable element (forinstance, a spring), with a hard length limited to set the max elasticlimit, as this thruster-to-externally carried section distance changesto a lesser degree with the angle of the balloon. This vertical tetheris able to carry some lift from the balloon as well as maintaining thethruster horizontally.

All of these tethers—the two main lines and the two verticaltethers—could be set as doubles for additional safety, meaning that tworedundant tethers are used in each line, and two pulleys are used ineach joint. This ensures that the loss of any one line section does notcause the whole branch network to fall apart. This could be easilyvisually monitored both in the air and during the refueling step, toinstitute repairs whenever a damaged section is observed. The mainvertical tether will also be designed to keep the externally carriedsection largely horizontal should one of the sides of the two maintethers be damaged. This will allow the system to use the paraglidingwing and thrusters to controllably return to the station.

Wings

FIGS. 6A and 6B are schematic diagrams showing a wing seen from thefront of the platform, unfurled and being used for steering (FIG. 6A),and the wing pulled in tight and cinched down (FIG. 6B). A singlewing-like structure can be attached to the main tethers below theballoon, and controlled by motors on the externally carried section. Thepurpose of the wing is twofold, to provide fine control during descentfor the airborne floating solar energy facility, and to guide the keelafter emergency detachment.

The wing may be structured like a paragliding wing which inflates to asemi-rigid airfoil shape via wind flow into and over the wing. The wingis held in place via two mechanisms. The first mechanism, tetherbearings, anchors the wing from moving around in the x−y plane, out fromunder the balloon. The second mechanism, tension lines, control theangle and twist on the wing, as well as pulling it in or releasing it tospread wide.

There are several possible methods to design the wings, with the majorvariation being the first mechanism, the tether bearings. As oneexample, for a rearward tail fin design the first mechanism is composedof linear bearings, such as rings, at two locations on the trailing edgeof the wing. These locations may either be the trailing two corners ofthe wing or may be symmetrically located (along the center-line of thecraft) but shifted in towards the center of the wing. These linearbearings are allowed to slide along the rear-two main cable tetherslinking the balloon to the externally carried section. This firstmechanism (tether bearings) may not be required, as the paragliding wingcan be released and operated under the balloon without direct connectionto the main guide tethers. The difficulty with the untethered version isensuring that the wing can be tightly bunched up after use to avoid windgusts from catching on the wing and causing unexpected dynamics. By wayof non-limiting example, the wing is attached to the main tethers and/orballoon using another set of lines or bearings, but several designs arepossible. A possible layout for a rigid-wing design includes running twoparallel cables from front to back, with both ends of the cable attachedmidway between the main cable's balloon and tank attachment locations.The wing is then attached to these two parallel lines so it cannot beshifted in the x-axis, can be pulled a small amount in the y-axis, andcan be easily warped to generate θ−x axis torque or angled to generatelift. This design may use rigid bars (or multi-segmented rigid bars)along the leading and trailing edge of the wing, which by default holdsthe wing flat and level. The parallel lines would be attached to therigid bars. This immobile attachment location method means the wingangle of attack is set by the balloon orientation angle, and so tochange lift, the whole balloon would be rotated. This design will havedifficulty detaching in an emergency as noted below.

As it stands, the balloon will act as a moderately good wing, so themajor use for the wing is steering rather than lift. This leads thedesign to focus on the rear-ward attachment method, which is simple butwould have difficulty due to unbalancing the system if generating largelifts. In an emergency, the main balloon-tank tethers can be cut,allowing the tank to fall away from the balloon. The wing will remainconnected to and controlled by the tank, becoming a parachute to controlthe fall and guide the landing of the tank.

The wing is attached via bearings to the back two main cables, stillunder the balloon but in the rear of that area. The two bearings allowthe wing structure to change θ−x, θ−y orientation, or even be pulled in,but not to move sideways or blow away. The rearward location of the wingholds it above but behind the main weight, the externally carriedsection. This means that during descent, if the wing is used to generatelift, it will generate a torque around the x-axis of the system. Thisshould not be an issue, as the drag on the balloon does likewise andwould partially counter this effect, and then the externally carriedsection location would shift relative to the balloon lift vector, fullybalancing out the torque. The net result would be a slight anglingdownward of the balloon to achieve equilibrium, which may be fixed byrotating the balloon around the x axis.

The second mechanism of wing control (tension lines) is composed of atleast two but generally four sets of tension lines running fromactuators on the keel out to the edges of the wing. These arecontrollably differentially released or drawn in to drive at minimumtwo, but generally four possible motions, requiring at least equalnumbers of independent actuators. The four possible motions are the 1)θ−y (can be ignored as lift generation can be done by the balloon), 2)θ−x orientation (of limited use), 3) warp of the wing in order to steerthe airborne floating solar energy facility, or 4) pull-in. The finalmode is where the tension lines can all be simultaneously be pulled into force all the corners of the wing to slide along the main linestowards the center and the externally carried section, essentiallyforcing the folding up the wing. A fifth actuator can be attached to aline that passes through a number of sliding bearings (for example,rings) along the edges of the wing, and when this is drawn in, itcinches down the wing down to the externally carried section so itcannot catch the wind. This is referred to as “pulling in” the wing, asshown in FIG. 6B, and reduces problems with wind drag during periods ofgeo stationary operation.

Solar Energy Capture

Solar radiation is captured via photovoltaic (PV) solar panel elementsattached to the upper surface of the balloon forming a photovoltaicarray (PV array). The PV array provides electricity to anelectro-chemical cell, which is mounted in the keel. The solar elementstransfer the solar energy to the electro-chemical cell and to theplatform for operation. The excess heat generated as waste by the solarcapture elements may also be captured via thermal-energy transfersystems, and turned into usable energy for use on the solar energyfacility or for storage in the electro-chemical cell.

The PV solar panel elements can take different forms, which include, byway of non-limiting examples, crystalline or multi-crystallinephotovoltaic cells, thin-film photovoltaic cells and other types ofphotovoltaic collectors. Concentrated PV systems, such as inflatableconcentrators with low mass may also be useful for increasing the powerto mass ratio. These are known to operate at higher efficiencies underintense sunlight. Should alternative solar energy capture technology bedeveloped, the PV units may be replaced without materially affecting thedesign.

In one non-limiting example mode, the airborne floating solar energyfacility has “hard point” attachments, to which are mounted one or morePV arrays. The PV arrays may be, by way of non-limiting example,conventional, rigid, small (less than 1 m²) crystalline ormulti-crystalline photovoltaic cells laminated between flexible sheets.

In another non-limiting example mode, the solar energy facility has aseries of flexible thin-film photovoltaic cells forming the photovoltaiccollector array mounted either to hard point attachments or directly tothe balloon's outer envelope, providing electricity to theelectro-chemical cell. These solar arrays are also flexible and so willnot generate significant stress concentrations on the inflated balloonsurface.

The keel tethers are used to shift the balloon so that the photovoltaiccollector array is optimally aligned with the sun. In one non-limitingexample, the mounting of the photovoltaic collector array centers thephotovoltaic collector array at close to 45° from the top position in amanner to configure the airborne floating energy facility to achieve theoptimal position with respect to the sun with a minimized range oftilting of the airborne floating energy facility. There are otherconfigurations which are possible, such as having the photovoltaiccollector array at close to 30°, or at another angle. Given that theincidence of solar energy will not fall significantly below 90°, thereare practical reasons to configure the externally carried sectiontethers and the photovoltaic collector array at a location higher than45° from the top position.

In another non-limiting example, the photovoltaic collector array isconfigured so that portions of the photovoltaic collector array areseparate from the fabric of the outer envelope. Other configurationshave the photovoltaic cells aligned in a common direction, so that someof the photovoltaic cells receive light normal to the surface of theouter envelope below the cell, but cells closer to the top or furtherfrom the top are angled relative to the balloon skin to receive light ina common direction. In other words, the photovoltaic cells in thephotovoltaic collector array are configured to receive optimally lightin a common direction.

The energy capture elements (PV solar panels in one non-limiting examplemode) should be pointed at the sun for the best efficiency conversion.This requires tracking the sun from the horizon, up to its zenith andback to the opposite horizon. As shown in FIGS. 5A-5C, tracking thesunlight from the horizon to vertical is achieved by changing the angleof the balloon. After noon the sun starts to set, and the solar energyfacility flips 180° in θ-z, and again uses the angle change to trackback down to the opposite horizon.

Given the arbitrary orientation of the balloon, a simple solution totracking can be found in flipping the balloon orientation 180° around anaxis normal to the earth's surface when the sun is at its zenith, andfollowing the sun back down to the horizon. This rotation and thecorrect orientation are effected by the thrust units attached to theballoon. This reduces the required tracking motion from ±90° rotation asused in a grounded system down to only 0 to 90° rotation. The requiredrange is thus halved. While the standard design plan as conventionallysuggested would call for placing the solar panels at the top of theballoon, this requires the largest rotation of the balloon to track thesun down to near the horizon, 90°. Large rotations may be problematicfor the design as they require significant distortion of the balloon andcomplex extra tethering. It is instead advantageous to have a smalleramount of rotation which is split to occur in both directions. The solarpanels can be placed at 45° down the side of the balloon, reducing theneeded rotation to only ±45°. The range can be cut yet further byaccepting a slight loss of solar power while the sun is at the horizon.For instance, if the solar panels are at approximately 30° off vertical,and the balloon is designed to rotate by approximately ±30°, then thesolar panels only see approximately 13% energy reduction while the sunis at the horizon. In one non-limiting example mode, the balloon istuned for the 30° off vertical concept, as shown in FIGS. 5A-5C. Thetradeoff is a few percent of the possibly daily energy capture vs themechanical design needed for large balloon angle rotations. The 30°off-axis with ±30° rotation concept is able to capture about 98.5% ofwhat is possible with the full 90° rotation. This is because thenon-normal irradiation only occurs for a short period during the day,and only for relatively small angles off-normal. The gain is that theballoon distortion at ±30° is a significant reduction from ±45°,exposing significantly less cross sectional area to wind, and reducingthe variation in the load path angle that the main keel tether line musthandle.

The main rotation of the balloon occurs around the y-axis, which istransverse to the long axis of the balloon. Most designs operate byrotating mainly or only around the x-axis, the long axis of the balloon.This has the unintended consequence in the tropopause of forcing theballoon to point its long axis north-south, which is perpendicular tothe general direction of the prevailing winds (east-west). This issuehas not been generally noted by other high-altitude platform designers,leading previous designs to focus on x-axis rotation for solar tracking.When the rotational axis is transverse to the long axis, the balloon can“point” into the wind (east-west) while simultaneously tracking the sun.This significantly reduces the average drag both due to the aerodynamicshape and the reduced cross-section. The balloon can be rotated bydriving the keel along the two main tethers slung below the balloon,changing the center of mass and thus the equilibrium rotation of thestructure.

A secondary rotation around the θ−x axis may also be implemented via thesame general mechanism that drives the primary θ−y rotation. The twoDegree-of-Freedom (DOF) rotation capability would provide moreoperational flexibility for the system in high wind scenarios. Thesescenarios require that the balloon balance between pointing into thewind and pointing the solar panels at the sun. A one-DOF θ−y system isable to efficiently track the sun and face into east-west winds, but itwould compromise on either wind resistance or solar capture fornorth-south winds. A 2-DOF capability provides a second DOF, that of θ−xthat allows the balloon to efficiently track the sun while facing intonorth-south winds. The combined system gives the most flexibility forhandling both solar tracking and wind resistance mitigation.

The mechanism by which this two-DOF rotation could be enabled is a setof four motors and spindles on the main keel mass, where eachmotor/spindle set is responsible for setting the tether length of one ofthe four lines coming down to the keel from the balloon. The keel can bedriven in the x axis direction (and thus force +θ−y rotation) viasynchronized motion of the four motors, rolling in tether on the twomotors on the +x side and releasing tether on the two motors on the −xside. The keel may be driven in the y axis direction (and thus force+θ−x rotation) via synchronized motion of the four motors, rolling intether on the two motors on the −y side and releasing tether on the twomotors on the +y side.

This rotation control mechanism provides one more DOF that may be usefulduring flight, that of synchronized intake or release of the tethers onall four spindles, resulting in z axis motion. The release of thetethers would provide a means to do the emergency separation betweenexternally carried section and balloon. The uptake may have some utilityfor stability of the floating solar energy facility during landing.

The solar energy capture elements will generally need to dispense withwaste heat. In the case of one non-limiting example method of PV solarpanels, these panels are more efficient at lower temperature, so thereis a benefit to finding an effective cooling technique for the solarpanels. Radiative heat transfer as well as natural and forced convectionwill all help dissipate the waste heat.

Forced convection over the solar panels is a promising method; however,if the solar panels are directly glued to the surface then the forcedconvection can only act on one side of the solar panels, which halvesits utility. By raising the solar energy capture elements slightly abovethe surface, perhaps on the order of a few cm, a channel can be createdbetween the underside of the energy capture elements (PV solar panels inone non-limiting example mode) and balloon surface. The energy captureelements should be anchored to the balloon via a mounting structurewhich allows air flow to pass in any direction, given that the directionof air flow may change through the day. A good example of this would bean array of posts. A raised lip may be placed around the edges of thesolar panel array which would serve to capture and slightly compress theair flow, forcing it to flow faster than the standard balloon-skinsurface air flow. This would be a further amplification over thefar-field air flow, as the air is forced to move more quickly to getover and around the balloon. Such omnidirectional air-flow withamplification will help drive the solar energy capture elementtemperature down to the ambient air temperature, as desired. Thestructure will have the additional benefit of decoupling the solarpanels from the balloon skin, protecting the balloon skin from damageand the capture elements from thermal expansion/contractionincompatibility issues. The mounting will also make it easier to repairor replace the solar energy capture elements. Finally the mounting hasthe potential to be used as a heat sink for the solar panels by properselection of shape, material and interface. This could potentiallysignificantly increase the solar panel's ability to dissipate heat tothe air running between the solar panels and balloon surface.

Energy Storage

The hydrogen approach envisioned design of the energy storage refers toa structure made up of one or more tanks. These tanks include i) onetank for each of the low energy precursor chemical(s) used for makingthe high energy fuel, and ii) one tank for each of the resulting highenergy fuel chemical(s) produced by the electro-chemical cell when inenergy storage mode. These fuels are storing chemical potential energywhich can be released as needed to provide energy, acting as a supplyfor power when the solar panels are insufficient. The chemical potentialenergy may be in the form of a battery or in the form of chemicallyseparated gases such as hydrogen and oxygen generated from waterelectrolysis, among other techniques. The majority of the stored energyis supplied to the ground station upon return to the ground, thuspassing off the energy captured by the platform in any of several waysincluding i) transfer of the energy via electrical means, ii) transferof the high-energy fuel chemicals, or iii) transfer of the tankscontaining the high-energy fuel chemicals to be replaced by empty tanks.

In one non-limiting example mode, the energy storage system isimplemented using three separate tanks—one for water, one for hydrogenand one for oxygen. The hydrogen and oxygen tanks may be type IIIpressure vessels (metal liner with fully wrapped composite) attached tothe balloon from below by tethers. The metal (for example aluminum)liner reduces hydrogen permeability while the composite (for examplecarbon-fiber) acts as the load bearing component. A layer between thebarrier and load layer may act as a self-healing material to plug cracksby solidifying upon contact with air or hydrogen, but otherwise wickinginto small gaps. It is alternately possible to use one of the fuelchemical tanks, e.g., the hydrogen tank, to store the water.

In one configuration, all of the chemicals which pass into theelectro-chemical cell and come out of it are stored on the airbornefloating solar energy facility. It is advantageous that all of thechemicals which pass into the electro-chemical cell and come out of itare stored on the airborne floating solar energy facility, so there isno change in system mass caused by the chemical energy storageoperation. This mitigates buoyancy variations. Variations in buoyancy ofthis sort generally require increased capability for lift gas storage,or increased balloon fabric gauge pressure, increasing system weight andlikelihood of failure. Additionally, the generated chemicals are oftenvaluable commodities, so storing them provides a financial benefit too.In one non-limiting example mode, holding onto the oxygen keeps thefloating solar energy facility mass constant and provides either a fuelimprovement or a source of revenue.

In an alternate example, water may be collected in the troposphere asthe floating solar energy facility rises. This would have an advantageif there is a reason not to carry water as a precursor from the ground,for example if the high energy fuel were discharged prior to landing thefloating solar energy facility. Alternatively, if the floating solarenergy facility remains within the troposphere, moisture cancontinuously be collected. If extraction of moisture requiresrefrigeration, this would reduce the efficiency of energy conversion,but may allow an increase in the total amount of high energy fuelextracted.

In one non-limiting example mode, the first and smallest tank containsthe water to be converted to hydrogen and the electrolysis unit. Thechamber containing water should be kept above freezing, or at leastbrought above freezing when the electrolysis unit is ready to operate inorder to maintain liquid water for the electrolysis unit. The watercould be maintained at temperature via a small heating unit andsufficient insulation. The oxygen produced by the electrolysis unit isconveyed to the oxygen tank. The hydrogen produced by the electrolysisunit is conveyed to the hydrogen tank.

The pressure generated in the fuel tanks should be kept largely equal,so that there is not a significant pressure differential between the twosides of the electro-chemical cell. This simplifies operation andminimizes diffusion, particularly in the case of one non-limitingexample mode of hydrogen generation via electrolysis. The pressure canalso be communicated to the precursor (water) tank via a fluidicconnection, so that either or both of the gasses pressurize theprecursor chemical (water) and thus avoid the need for pressurizingpumps. In one non-limiting example mode, the gases may be kept separatefrom the water by a flexible membrane which passes the pressure forequilibration, but does not allow diffusion of the gas into the water.Such a setup ensures all chemicals—precursor and fuel—are at roughlyequal pressures, which reduces the need for heavy and expensive pumpingequipment. Any fuel chemicals in the precursor tank would be driven outwhen the precursor tank is refilled at the ground station, thus ensuringcomplete recapture of the fuel chemicals.

The hydrogen chamber does not require heating and in fact benefits fromthe cold temperatures at altitude as this enables near cryogenichydrogen storage with an associated increase in gas density. Thehydrogen tank can be wrapped in insulation so that it stays as cold aspossible, close to the −60° C. typical of the tropopause. This increasesthe storage density of the hydrogen both at altitude and when the solarenergy facilities return to the station. The solar energy facilities aredescending for approximately an hour, at low altitude for a short time(<0.5 hr) for the material transfer, and then ascending forapproximately another hour, meaning that the insulation only needs tokeep the temperature low for a limited period of time before thehydrogen is drained and replaced with water. The excess heat generatedby the electrolysis unit is stored in the water to aid in overnightwarming or dissipated via external heat fins. Thermal-energy conversiondevices such as thermoelectric materials or Stirling engines can be usedto recapture some of this waste heat and turn it into usable power toimprove the overall system efficiency. The two chamber system keeps thehydrogen pure so that it is suitable for distribution and also reducesexplosion risk since there is no oxygen entering the hydrogen section ofthe tank.

The water tank can be surrounded by an insulation layer of air, whichwill help reduce the power required to keep the water liquid duringperiods of no access to solar power. This may be done by the use ofclosed cell insulation, which is pressurized such that it achieves fullvolume only at maximum altitude. Closed cell insulation would belightweight, low cost and would provide high thermal resistance due tothe use of air as the insulation. The water may be used as a thermalcapacitor to keep the electronics and other sensitive equipment withinoperational temperature bands overnight. This can be tuned via thethermal insulation.

In the battery example of energy storage the electricity from the solarenergy capture system is used to charge batteries. A depiction of thisconfiguration is shown in FIG. 7, in which an airborne floating solarenergy facility 700 has a keel section 702, which includes a batterycarrier 712. In addition to carrying batteries, airborne floating solarenergy facility 700 can be configured to carry and produce high energyfuel or lift gas, which can be stored in storage tank 742.

The system as depicted in FIG. 7 can also function with inertial massesin lieu of batteries, with the storage units representing the inertialmasses.

Balloon Gas Compression

In a non-limiting configuration, at least two compression units are usedin the design. The first compressor transfers lift gas between theballoon and the lift gas storage tank, if used in the closed-cycledesign noted earlier. This first compressor is used to control the massof lift gas in the balloon, all of which is generally at a constantoverpressure of around 1 kPa, to the environment. This results in thehydrogen providing a nearly constant lift per mass largely independentof altitude and temperature. The second compressor, specifically an airblower, drives ambient air from the surrounding environment into theatmospheric diaphragm of the main balloon. This air blower is used tocontrol the pressure of the main balloon to the targeted overpressurevalue which directly determines the stress in the balloon fabric. Athigh pressures the balloon acts as a rigid structure, which is crucialfor supporting the solar energy collection elements and forming a robustaerodynamic structure; however, if the pressure is too high the skinwill be damaged. By actively controlling pressure to a safe value (oreven raising it temporarily during specific events like high winds) theballoon design can safely navigate the balance to gain the advantages ofthe lightweight inflated-rigid structure without risking damage to theballoon skin.

The lift gas tank (holding hydrogen in one non-limiting example mode) ispressurized to the scale of 20-100 bar in the example mode, a valueknown to be within the bounds for the direct output of the electrolysisunit (the electro-chemical cell of the example mode) to operate at highefficiency. The tank mass can be shown to be approximately constant,independent of pressure, suggesting that there are not significant masssavings to be had by further pressurizing the gas. Instead, this higherpressure simply requires more equipment and power to drive the hydrogen.The 20 bar scale can be generated without any special compressionequipment after the electrolysis unit, and so it serves as a convenientupper bound for the tank pressure from a viewpoint of simplicity. Thehydrogen compressor is used to control the amount of hydrogen in theballoon, which is directly proportional to the lift force generated bythe balloon (via the balloon design described previously). In theexample mode, the hydrogen tank thus serves dual purpose as 1) a storagefor the chemical fuel generated by electrolysis and 2) as the necessarythird or additional compartment for the lift control mechanism.

The hydrogen compressor can be of a design that can be used to recaptureenergy when allowing the gas to leave the tank. A double acting pistondisplacement pump would be able to control flow into or out of the tank.Gas leaving the tank can be used to run the pump motor as a generator,recapturing a fraction of the energy. This reversible operation isexpected to capture approximately 30% of the energy invested incompressing the hydrogen.

The second compressor, an air blower, is used to drive gas from theambient atmosphere into the atmosphere diaphragm in the main balloon,and is used to keep the balloon effectively rigid. The air compartmentwould be maintained at a slightly higher pressure (with present targetvalue ≈1 kPa) than the surrounding atmosphere. A high flow, low pressureair blower should be used for this operation. The hydrogen in theballoon will reduce in volume as the balloon descends, so the airchamber should be inflated to maintain consistent balloon pressure. Thehydrogen in the balloon will increase in volume as the balloon ascends,so the atmospheric diaphragm would be vented to the environment tomaintain consistent balloon pressure. This air blower may be anindependent element or may be built in as an auxiliary load driven bythe thrusters or primary compressor motor. Flow rate estimates for thepower draw of the primary lift gas compressor vs. the air compressorsuggest that the air compressor will only draw a few percent of theenergy of the lift gas compressor, and so could be added as an auxiliaryload draw on the lift gas compressor, meaning that for rapid pressurechanges, the whole power of the lift gas compressor can be driven intothe “air” compressor for short periods.

Electro-Chemical Cell

In the hydrogen approach, an electro-chemical cell is used to extractthe energy provided by the solar energy capture elements for storage inthe form of a high energy fuel, which in the non-limiting example ishydrogen. This is done by drawing in low energy chemical(s), addingenergy by splitting or combining, and storing the resulting chemical(s)as a form of chemical potential energy. A non-limiting example mode forthis is an electrolysis unit, used to chemically break apart the waterinto its constituent elements. A wide range of electrolysis technologiescan be used; however, the two most mature are PEM and Alkaline. Theexample mode utilizes a PEM unit as it is well suited for this designdue to its i) compact size and weight, and ii) can easily keep the gasesseparated, which aids in the purity of the product. The unit is attachedto or within the water tank. The hydrogen output is directed to thehydrogen portion of the tank. The oxygen output is directed to theoxygen container.

The low temperature of the surrounding environment can be used to aid inthe process of purifying and drying the generated gases. As compared togrounded systems, the low temperature environment at altitude providesan easy means to help the purification. An environmentally aidedpurification techniques such as a cold trap can reduce power draw, gasloss, system cost and weight. This is a non-intuitive opportunityspecifically created by the high altitude and cannot be exploited bygrounded systems. Typical system design would call for a heavy,expensive and lossy dryer/cooling unit. The example mode of suchenvironmentally aided purification is a three step process.

The first step is the flow of the hot, humid high-energy fuel gases(hydrogen and oxygen) through a series of cold channels which are heldat low temperature but above freezing by controlled thermal interactionwith the cold atmosphere. This low temperature tubing will act todehumidify the gas, and condense the moisture onto the channel surfaces,where it can flow back to the electrolysis unit. The channels should beheld above freezing to avoid generating an ice buildup which clogs thechannels. These channels are also intended to cool the gas to near 0° C.

The second step is carried out on the resulting gas flow from the firststep. The cool, dryer gases are run through multiple sub-freezing coldtraps. These traps are maintained at their temperature by controlledthermal interaction with the cold environment. The cold traps condensethe remaining moisture and other contaminants onto the sidewalls of thetrap. When the traps are full, such that the condensate is beginning tosignificantly impede further gas flow, valves can be used to block theentrance and exit of the “full” trap and it can be heated up until thecondensed moisture and contaminants are liquefied/vaporized. The liquidcan be drained back to the electrolysis unit, to ensure the whole cycleis closed and no chemicals are exchanged (in or out) with the externalenvironment. On rare occasions, the trap can be drained to theenvironment if needed, and purged with process gas once brought backonline. Once drained, the trap would be re-cooled to pull all remainingunwanted impurities again to a condensed state, and then the valveswould be reopened to restart the main gas cleaning process. Multiplecold traps in parallel would allow the system to continue to operatewhile one or more is out during the cleaning process.

The third step is carried out by exploiting the low temperature of thestorage tanks, which are designed to equilibrate down to theenvironmental temperature in order to help pack the gas more tightlyinto the tank. Such tanks are at significantly sub-zero temperature, sowill act like large cold traps. They will build up impurities on theirwalls and clean the gas further. The tank will stay at the lowtemperature upon return to the ground due to the insulation, so theimpurities will remain condensed. The tank may be deliberately heated,as during maintenance, and the impurities could be drained out the baseof the tank, or blown out in a fashion similar to water traps forcompressed air lines.

Thermal-energy conversion devices such as thermoelectric materials orStirling engines can be used to recapture some of the waste heatgenerated in the electrolysis process and turn it into power to improvethe overall system efficiency. The stored high energy chemical fuel(hydrogen and oxygen in the example mode) can be used to run theelectro-chemical cell (electrolysis unit in the example mode) backwardto supply backup power during night, landing or emergency situations.Since the reverse power draw is generally only a small fraction (about5% of the forward power flow), the reversible electro-chemical cell isable to generally run at higher efficiencies. In the example mode, theelectrolysis unit is able to operate at much lower current densities inthe reverse fuel cell state than in the forward electrolysis state.Alternately, a separate electro-chemical cell specifically designed forreverse operation could be used. For the hydrogen, electrolysis system,this would be a fuel cell.

In the battery approach, an electro-chemical cell is used to store theenergy provided by the solar energy capture elements for storage bycharging batteries.

Control Electronics

The electronics unit, including a GPS system, is the control nexus ofthe system, and is the active controller of the solar energy facilitylocation including communicating with nearby solar energy facilities,monitoring and controlling the pressure within the balloon, monitoringthe operations and status of all components, checking for errors, leaksin the balloon, leaks in all other systems, positioning the floatingsolar energy facility for solar tracking, communicating with the groundstation to coordinate landing, etc. The electronics could be located ina heated container next to the water tank which would likewise bethermally controlled.

Directional Control Mechanisms

FIG. 7 is a schematic diagram showing a landing sequence for docking theairborne floating solar energy facility. Attached to the floating solarenergy facility are at least two sets of directional control mechanismsor “thrusters”. One set is anchored to the side of the balloon, with onethruster on each side of the balloon, where only one of the twothrusters is shown in FIG. 1. The other set is anchored with onethruster on the front and one on the back of the balloon

The side thrusters point in the x-direction and drive the balloon alongthat axis. The side thrusters are on a gimbaled frame which can rotatearound the y-axis, to counter the overall balloon rotation as it tracksthe sun. This arrangement can be used to control the balloon to alwayspoint the thruster in roughly the horizontal direction. The thruster isallowed to rotate around its contact point with the balloon, but isattached to the vertical tether coming from the side of the balloon, soit is always held largely horizontal. This allows for a gimbaled systemwithout the active actuation.

The second set of thrusters are located on the front and back ends ofthe balloon, are pointed along the y-axis, and generates thrust alongthe y-axis. These could be likewise gimbaled if the balloon is intendedto also rotate around the x-axis. The second set of thrusters is used inconjunction with the x-axis thrusters to generate thrust in anydirection in the x−y plane. The balloon and solar energy collectionelements must face the sun to collect energy, but the wind direction mayapproach from any direction. Therefore, the combination of fourthrusters provides arbitrary counter thrust to resist the wind, but doso without generating a torque on the balloon, and hold the floatingsolar energy facility stationary regardless of the wind vector. This iseffective during the generally geostationary energy collection phase.During landing, these thrusters may also be used to aid in the controlof the descent and docking.

The thrusters may be anchored to the balloon using a plurality oftensioning cables running in loops making contact with the surface ofthe thrusters opposite the balloon. Each thruster is attached to acompression bar which is pressed against the surface of the balloon atone end, and attached to tensioning members at a point near the far end.These loops, once tensioned, will compress the bars against the inflatedballoon skin. The thrusters are attached to the compression memberbetween the balloon and the tensioning cable anchor point. By having thethrusters closer to the balloon than the tensioning cables, the loadingon the bar is minimized. Loading between two anchoring points is anadvantage over cantilever loading. Additionally, this places the tensioncables as the furthest out elements, which can act as protectivebarriers of the last resort to reduce the chance of the balloon beingdamaged in the case of a collision.

The loops are attached to the balloon skin at points between thethrusters, approximately midway. In this area, the cables are sittingtangentially to the surface, so a simple surface clamping structure willanchor the cable to the floating solar energy facility. By using anearly continuous loop running around the balloon, the tension in thecable does not need to be passed to the balloon skin; this avoids highstress spots on the skin. Several loops would be run around the balloon,to cross over each thruster so as to provide anchoring in bothdirectional axes on the surface. An example layout of the tension wiringis shown in FIG. 1. For the thrusters on the sides (middle of theballoon as depicted in FIG. 1), the compression member also serves as arotary axis around which the thruster can rotate. This allows thethruster to generally point horizontally, even when the balloon isrotated. This rotational attachment technique can also be used for thefront and back thrusters if the balloon design is intended to carry out2DOF rotation.

Applications

This platform is usable for a wide range of applications. This systemmay, by way of non-limiting example, be used for energy harvesting, asdescribed in detail in the energy harvesting operation section. Otheruses of the platform include long duration, large payload operationssuch as surveillance, monitoring, telecommunications. The low powerrequired to hold position by the airborne floating solar energy facilityplatform is another advantage, due to its airship design it is able tostatically stay aloft. An alternate use for the platform would utilizethe energy capture capability to continually charge the batteries inorder to provide a continuous supply of power to both the thrusters andthe externally carried section. Such operation would enable the platformto go on indefinite duration trips while supplying large payloads withhigh power draws. The cyclic operation scenarios would have a base ofoperations for the school of platforms, where air control sensors suchas radar may be used to establish the location of the school and providesense-and-avoid capability for the school against other air traffic.

Energy Harvesting Operation

There are four phases of operation: liftoff, harvesting, landing, andenergy transfer. Each phase of the operation is described below.

Liftoff

FIG. 9 is a schematic diagram showing the control of the airbornefloating solar energy facility. Flight operations and control oftransfer of energy is performed by an on-board controller 911, which isresponsive to a master controller 921 at a ground location. Additionaloperations, such as docking control can be executed through the mastercontroller or separately, as for example, through docking controller935.

At the beginning of the cycle the solar energy facility is prepared fortakeoff. The system is provided with a full supply of low-energyprecursor chemical(s). For one non-limiting example mode, the systemstarts with the batteries effectively empty or fully discharged. A smallamount stored energy may be retained for drone operation. The balloon isfilled with enough lift gas to provide liftoff with the desiredvelocity; the remaining portion of the balloon is pressurized with airfrom the atmosphere.

The balloon is released from its mooring and rises vertically into theair. As the balloon rises, the lift gas will take up more space in theballoon. Air is vented from the air side of the balloon to maintain aconstant slight overpressure while avoiding the excessively highpressures that could result in balloon burst.

When the balloon reaches the harvesting altitude, the lift controlsystem zeroes out the lift force. Either enough hydrogen is removed tobring the balloon to neutral buoyancy, or the balloon pressure isincreased to raise the mass of the balloon, or both are used. Air ispumped from the environment into the balloon to compensate for theremoval of the hydrogen and maintain the balloon pressure at a targetvalue.

Energy Capture

During harvesting the floating solar energy facility maintains a fairlyconstant altitude. This altitude is currently envisioned to beapproximately 17-22 km, known as the tropopause. This is above airlinetraffic, the jet stream and above 90+% of the atmosphere. Altitudeadjustments are made by varying the lift gas or air mass in the balloon.Lateral adjustments are made by the use of the thrusters, which are ableto drive the solar energy facility at greater speeds at high altitude.

Throughout the day, the balloon is rotated to face the solar energycollection elements (photovoltaic cells in one or more photovoltaiccollector arrays in one non-limiting example mode) at the sun. Theballoon tilts about the y-axis through the keel being driven along thecabling system. The solar panels are placed at about 30° off of thehorizontal top surface, and the balloon will capable of further tiltingabout 30° downward to point the solar energy collection elements a totalof 60° off of vertical. This allows the balloon to catch all but theearliest of the sun's rays at near normal incidence. After noon, theballoon spins 180° around the z axis and tracks the sun down the otherside. Thus near full tracking is achieved with only 30° of rotation,which is relatively easily achievable with only shifting the keeldistribution. The balloon is rotated, and absolute location ismaintained, if necessary, by the fans/thrusters on either side.

The energy from the solar energy collection elements is used to chargethe electro-chemical cell, which stores the energy. In anothernon-limiting example mode, electricity from the PV solar panels is usedto power an electrolysis unit. The electrolysis unit converts the waterto hydrogen and oxygen. The oxygen is stored in its own container. Thehydrogen is stored in the hydrogen portion of the tank. As the water isconverted to gas the mass in maintained. Harvesting ends when the wateris almost completely consumed.

Landing

Landing is started by removing lift gas from the balloon or increasingair mass until the floating solar energy facility starts to fall. Thewing cables are released such that the wings can inflate. Direction iscontrolled by changing the angles of the wings through the wing cables.The descent speed is controlled through the rate of hydrogen beingpumped from the balloon to the tank.

FIG. 8 is a schematic diagram showing the floating solar energy facilitylanding, automated capture, refueling and release.

Upon reaching the ground station, the mobile solar energy facility iscaught by a mobile ground platform and transported to the fillingstation. Initially, the solar energy facilities may guide themselves orworkers may guide the floating solar energy facilities, pulling them tothe correct station. The floating solar energy facilities are controlledto be neutrally buoyant or slightly heavier than air so they should bemanageable by a worker or worker and automated unit. Eventually, thisprocess will need to be automated to meet the power demands. This wouldinvolve a landing runway type setup, where the solar energy facilitiesfly in at a shallow angle, and a ground cart, possibly on a track,catches up to equalize speed with the solar energy facility. Contact ismade, and the ground cart now drives the mobile solar energy facility toa cradle.

Fuel and Precursor Transfer

At the cradle, the floating solar energy facility is moored. Themajority of the fuel—in the example mode, hydrogen and oxygen—is removedfrom the floating solar energy facility by either a mass transferprocess for the attached tank or a tank switching process to remove theproduct-filled tanks and replace them with feedstock (water)-filledtanks. This process leaves enough lift gas for powering the ascent andenough stored energy to operate the drone as it returns to altitude. Thefloating solar energy facility is checked and any needed regularmaintenance is performed. Just prior to takeoff, lift gas is added tothe lift gas chamber or air mass is removed from the balloon to createthe takeoff force.

In the case of energy storage with batteries, the batteries may bedischarged or may be transferred and replaced with previously-dischargedbatteries.

Ground Station Layout

The ground station can be either located on land, at sea, or in the airif desired. The station is envisioned as a several segment structure.First, the airborne floating solar energy facility is captured by thecapture structure, which in a non-limiting example is a ground capturevehicle. The solar energy facility (no longer airborne) is then shuttledto a docking structure, “cradle”, where it is inspected, emptied andrefilled. Finally, the solar energy facility is shuttled by the groundcapture vehicle to the exit, where it is released for return flight.

It is noted that the capture systems aid in landing the drones, whilethe cradle systems deal with the energy transfer. The capture systemsmay be mobile vehicles, while the cradle systems are often stationarydocks.

One instantiation for the station is to operate in a linear fashion. Atone end, the floating solar energy facilities are captured, then theypass through a large structure where maintenance and masstransfer/inspection is carried out, then they are passed to the otherend where they are released. Multiple main axial rails would run thelength of this setup, with cross-connects so the floating solar energyfacilities and ground capture vehicles could be routed around damage. Ina non-limiting example, this would use at least two lines, and possiblythree or more lines. The capture and release ends of the station wouldbe made symmetric, so if the wind direction changes, then theorientation of the station can be changed without issue. They could beraised by about the height of the balloon about 15-30 m, so if thefloating solar energy facility misses, it can fly over the stationwithout crashing, and ii) the station entrance tubes are out of thewind. In one configuration, the station can be raised by use of a gantryor earthen berm.

Another instantiation of the station is to operate with a generallycircular layout. The main station is under a flat roof that is at leasthigh enough for the floating solar energy facility to pass under it withclearance. The flat roof is the capture and release area. The edges ofthe building are sloped so that floating solar energy facilities andground capture vehicles can be driven up and down the slope, perhaps ataround 45°. Once the floating solar energy facilities are captured, theyare pulled in parallel with the wind until the ground capture vehicledrives off the edge of the roof and into a trench area around thebuilding. The trench is formed by the sloped edge of the building on oneside and by a wall on the other side. The wall around the main buildingis as high as the flat roof. The outer face of the wall (away from thebuilding) may be a likewise sloped surface so that wind hitting the wallis directed up and over, as well as any floating solar energy facilitiesthat collide with the wall. The wall is a distance away from the edge ofthe main building so that at least one floating solar energy facilitycan pass along the trench, or two. The outer wall may be hollow withonly the sloped outer surface covered. Then multiple floating solarenergy facilities can pass around one another when traveling in the gaparea between the building and the outer wall. Once the floating solarenergy facility and ground capture vehicle is pulled off the roof, it isbrought into the main building, where a grid of floor and ceiling railswith mounting points can guide the floating solar energy facility to anyof a grid of docking systems. Additional space may be used formaintenance and storage. Once the floating solar energy facility isemptied and refilled, it is shunted back out to the trench via groundcapture vehicles, and it is then brought back into the wind and releasedonce it has positive buoyancy so it will rise. One possible distributionlayout is to have the floating solar energy facilities being capturedalong an axis parallel to the wind passing through the center of thestation. The floating solar energy facilities then fly in from upwind,get captured and get pulled down in the downwind section. The floatingsolar energy facilities ready for release are brought to the other twoquadrants of the station (left and right), and either released in thetrench or brought to the roof. There may also be a hole in the roof atthe center of the station, so it forms a donut. Then arriving floatingsolar energy facilities come in from upwind, are routed to the centerhole and down, then when ready for release are routed back up the centerhole or sides and released at the downwind end.

Another instantiation of the station is to have a widely separated setof capture systems that are combined with cradles, so the drone blimpchooses with station to land at, halts there for the duration of theexchange, then takes straight off from the landing spot. This has theadvantage of simplicity, but requires a significant amount of spacingbetween the stations to allow for other drones landing. The landing andlaunch patterns would also be intermingled, which could cause accidents.However, in areas with significant space, this may be a simpler design.For instance, if the operation is carried out over the ocean, smallplatforms could be deployed as capture and cradle combined, and thenwidely separated. Systems (boats) could shuttle tanks/batteries betweenthese platforms. This would provide a simple, scalable and robuststation out over the water.

For a 1 GW station, the capture region might be 300 m×300 m, or about0.1 km². The main building would have a grid of about 80 cradle systems,perhaps distributed as a 10×8 grid, with the 10 length being parallel tothe main axis of the station. Each cradle system would be separated bymore than the diameter of the balloon, so that a floating solar energyfacility could be docked at each without collision. Main rails would beinterspersed between the grid of cradles, with 8+1=9 main axial rails,each separated by perhaps 50 m, for a total dimension of 350 m long, and450 m wide. The release region would be made the same size as thecapture region. Maintenance and storage may be carried out on the floorabove or below the main bay. This size is comparable to 2 km² for a 1 GWnuclear power plant or about 30 km² for al GW of ground-mounted solararray.

Capture and Cradle Systems

The grounded station will have two major systems among others. These twoare the capture system and the cradle systems. The capture systems arespecifically designed to capture the incoming floating solar energyfacilities during their landing efforts. The capture systems aregenerally referred to as vehicles as in “ground capture vehicle”, but alater instantiation notes that they can be operated as immobile systems.A second set of systems, the cradle systems, are separate from thecapture system and perform a different role. The cradle systems carryout all of the energy (tank, chemical, etc.) transfer onto/off of thefloating solar energy facility as well as inspection operations of thefloating solar energy facility. The cradle system is generally anon-moving station to which the floating solar energy facility isbrought. The cradle system specifically refers to the structure wherethe floating solar energy facility is brought to have the energytransferred out of it, and to be inspected for damage/issues.

While the capture and cradle systems are described separately, it ispossible to construct the capture system to include the cradle systems.

Capture

The capture systems have two main features, i) a means to attach to apassing floating solar energy facility, and ii) a means to anchor to thesurface below.

For the floating solar energy facility attachment, several devices mightbe used that would be capable of anchoring to the floating solar energyfacility. This may include an arm, a net or extended loop of tether, amagnetic grapple and/or a small quadcopter with a tether. Another optionis for the floating solar energy facility to have a possibly extendablerope hanging below it, which would have an attachment point at the endof it such as a loop or hook. The default technique may be for thefloating solar energy facility to drag a loop below it along the grounduntil the loop is caught on the ground capture vehicle. If this misses,the ground capture vehicle could accelerate to catch back up with thefloating solar energy facility and force an attachment. Once theattachment is made, the floating solar energy facility is reeled in andkeel mass is clamped down to the ground capture vehicle. The floatingsolar energy facility can be made heavier than air by the lift controlsystem (removal of lift gas or addition of air mass) in order to landquickly.

For the ground attachment, the ground capture vehicle would be able todrive along the ground and clamp down to anchored rails or use airbearings or some other technique to anchor to the surface. In onenon-limiting example the rail design is used, and in the capture area,the rails may be upside down T-shaped cross sectional metal extrusionsembedded in concrete. The anchor structure on the ground capture vehicleis a T-shaped bar that cannot be removed from the rail due to the armsof the T. The intersection of these extrusions is a gap that allows theground capture vehicle to choose which direction to go. The T may haverollers on the surface to avoid sliding. When under high wind load, theT-bar would keep the ground capture vehicle from being pulled off;otherwise it would ride along within the rail without significantfriction. This would keep the ground capture vehicles down and allowthem to change direction at intersections, but make them resistant tobeing blown away by high wind loads.

It is desired to have the floating solar energy facilities travelingwith the wind so as to ensure they have a velocity relative to theground. This is the opposite to the conventional technique ofapproaching directly into the wind. Conventionally, a landing airplaneis high mass, has significant kinetic energy and has a velocity that iswell above the wind speed, so approaching into the wind slows theapproach velocity relative to ground. For the floating solar energyfacility, the situation is reversed. The floating solar energy facilityhas little mass, little kinetic energy and can not necessarily generatea velocity exceeding that of the peak possible winds. It is thus simplerto approach by floating in with the wind, perhaps using the thrusters toadd to that velocity and control the position to ensure capture, andthen use the thrusters at the last moment to reverse thrust while overthe capture pad and attempt to hold position. The scale of the thrustersrelative to the floating solar energy facility mass are such that thedeceleration would only be a few seconds, unlike a conventional fixedwing aircraft. The floating solar energy facility would seek to alignits landing with the rails, so as to simplify the capture operation. Tothis end, the capture and release sections may have a cross-hatchedpattern of rails so the ground capture vehicles can travel in twoperpendicular directions. The floating solar energy facilities can thendrive with propellers to come in as close to parallel to these rails aspossible, while the ground capture vehicles synchronize speed to improvethe chances of capture. To maximize the chances of catching the floatingsolar energy facility, several steps would be taken:

-   -   Rails are arranged in multiple directions, possibly 0°, 90°, or        at 45° angle    -   Floating solar energy facilities align last part of flight to        the rails    -   Multiple ground capture vehicles may be tagged in to capture the        floating solar energy facilities if problems arise    -   The capture/release areas may be made large to give the floating        solar energy facilities sufficient time for engagement, perhaps        squares about 100-150 m to a side    -   As the floating solar energy facilities finally approach, they        can drive their thrusters in reverse to slow just when they        approach the ground capture vehicles.

The capture and release side would be switched as needed to ensure thatthe wind dot product with the flow of the station (from capture torelease) is always positive which means it is always helping drive thefloating solar energy facilities down the flow path.

Emergency ground capture vehicles may be deployed at the downwind end ofthe capture area with extra capabilities (tethered arrows, nets etc.) tograb missed floating solar energy facilities

The ground capture vehicle is used to decelerate the floating solarenergy facility and then guide it to the cradles. The ground capturevehicles are lined up in the upwind section of the capture region, andcan grab floating solar energy facilities as they arrive. If the windspeed exceeds the operating speed of the floating solar energy facility,the floating solar energy facilities will be able to come in with thewind to ensure they can reach the station. This allows the floatingsolar energy facility to approach with the wind if it is unable toexceed the wind velocity. Once the floating solar energy facility iscaptured, the ground capture vehicle will proceed down the main railstowards the main building. These rails can be designed to drop in heightto bring the floating solar energy facilities under cover from above andthe side, so as to get them out of the wind.

Another design would use parallel tracks in the landing/launching area,similar to the previous description. The ground capture vehicles couldbe configured to have a wide base to handle the very large balloon side.It could have a Y shape balloon catcher pointed vertically. The extremeend of the two arms would be configured to anchor to the front-backx-direction pointing side thrusters or compression bar. It is preferredthat the anchoring be to the compression bar or the tension wires,rather than to the balloon directly. This ensures the load passesthrough the designed hardpoints and is distributed by the preloadedwiring. As backup, loops hanging off the balloon could be slid ontohooks so the balloon is held even if the main Y-arms fail.

The attachment at the end of the Y-arms could be configured so that thewind pressure pushing the balloon horizontally would anchor it furtherinto the attachment point. The Y catcher could be rotated around itscentral vertical axis to be aligned with the wind direction. This wouldallow it to capture the incoming blimp regardless of which way the windis flowing. It would also allow the drone to be pointed into the windeven after it is captured, which ensures the wind pressure is kept to aminimum. When the blimp is to be released, the drone could be spunaround so the wind pulls it out of the attachment, or it could be leanedbackwards so the buoyant force pulls the blimp out. The cart could thenbe driven along the rails into the station while the drone blimp ispointed into the wind, whichever way that is.

Small drones on both the blimp and on the ground capture cart could beused redundantly to pass mooring lines, which could then be reeled in ifthe drone is going to miss the catch. The small drone on the blimp isthe same one that is described in the safety section for inter-droneredundancy, and both require the drone to carry a small tether. The Ycatcher would act like a target for the drone. If the blimp is not inline with the target, the rapid drones with mooring lines (travelingahead of the main blimp or held out in front of the target from theground) could be used to make a quick clip in, which could then berapidly reeled in to ensure the blimp passes into the Y-catcher. Thesmall drone on the blimp would be preferred, as it would float in withthe wind and the blimp. A simple technique would be to have a clip atthe end of the line that the blimp small drone can use to clip into aspool. As soon as this clip is attached, then the small drone releasesthe line and the spool pulls the keel in to an anchor point at the jointof the Y-catcher. A similar technique provides a configuration with theconnection drone being at the end of a tether with a clip, floatingabove the Y-catcher. The drone would chase down the incoming drone, clipto the keel and then be reeled in with the blimp into the catcher. Usingboth would increase the reliability.

Another mechanism that could be used to aid in capture would be anadjustable wind wall. The wind wall could be rolled around to bedown-wind at all times. This would create a turbulent zone ahead of thewind wall, where the wind velocity would be reduced. It would be easierfor the drone blimps to then glide into the dead zone, and be carriedout. The wall could be attached to a rail and be rapidly updated to bedownwind. Such wind walls could be placed equally on both the landingand launching sides. These would act to control wind flow over the areasas needed. This wall could have a net on it that could halt drone blimpswhich would otherwise have missed the landing operation. Also, thelanding small drone could be used to clip to the wall, providing a sixthmeans to effect capture. Finally the emergency ground-station dronesnoted in the safety discussion could be used to chase down the floatingsolar energy facilities which have escaped the other safety mechanisms,and possibly attach a tether to the floating solar energy facilities fora forced return to the station.

-   -   Y-catcher    -   Drone-based tethered drone makes contact    -   Ground-based tethered drone makes contact    -   Secondary Y-catchers    -   Blimp catches in net    -   Blimp drone-based tethered drone clips into net    -   Emergency drones based in the ground station catch and tether to        make contact

Transfer to Cradle Systems

Once under such cover, the ground capture vehicles could eithertransport the floating solar energy facility directly to the cradlesystem or pass it off to a more efficient rail transfer guide, which hasanchor points both above and below the floating solar energy facility(as well as rails both above and below). This ensures that the floatingsolar energy facility does not drag behind while being driven around.The two-point contact rail guide takes the floating solar energyfacility into the building and to a docking port. While the cradlestations may be laid out in any way, a simple form would be to have aline of cradle stations on either side of each of the main axial rails.Each cradle would be accessible from opposite sides by two main axialrails, and there would be redundant rails of each of the main axiallines to route around damage. By making it possible to pass over thecradle station areas, the floating solar energy facilities may be“hopped” or moved between main axial lines to route around damage.

The cradle systems would likely reach to the keel of the airbornefloating solar energy facility from the side and would extend out tomake the contact, thus allowing for the floating solar energy facilityto pass through the cradle station berth without contact if needed. Thefloating solar energy facilities would likely be maintained with theirlong axes pointed along the main rail axis to minimize rotation time, asthis would be a slow process. The ground capture vehicles would beseparated by slightly more than the length of the floating solar energyfacility.

Shuttle Vehicle

While the configuration described above relates to a fully functionalfloating solar energy facility being launched from and retrieved by aground station, it is alternatively possible to provide transportationof the fuel precursor and the produced high energy fuel with a separateshuttle vehicle. The use of such a shuttle vehicle has the advantages ofbeing optimized for transport, and does not necessarily requirephotovoltaic collector arrays or electrolysis equipment for generatingthe high energy fuel from the precursor. The shuttle vehicle ferries thematerials to and from the airborne floating solar energy facilities. Inaddition, it is possible to transport individual components to and fromthe airborne floating solar energy facilities, allowing for replacementand more efficient climb and descent profiles of the airborne floatingsolar energy facilities.

The precursor and high energy fuel can be transferred using tubing orother conduit, or may be transferred as a complete tank unit or as acomplete tank along with an energy conversion (electrolysis) unit, as anenergy conversion and storage system.

Repair and Storage

Floating solar energy facilities showing damage can be routed to aseparate area of the plant for maintenance, possibly up or down a level.This would require an elevator-like feature. The repair level wouldprovide both an area to do deeper maintenance/replacement as well as aregion to store the floating solar energy facilities during high windperiods. It may also be done in the main building, just to the sides ofthe main ground cradle stations area.

Fuel and Precursor Transfer Operation and Storage

The gas can be routed outside the main hangar building to a centralpurification and storage facility, which delivers hydrogen to either beused to generate power, or shipped off as a product.

The gas could be handled by moving around the tanks that are removedfrom the drone, so the fuel does not need to be drained andre-pressurised. This simplifies the system operation, energy demands andmaintenance by not requiring pumps

In one non-limiting example mode, the gases captured from the floatingsolar energy facility will generally need to be stored in order tosmooth out the input flow of gas. The platform produces a largequantity, and then deposits it as a sudden spike to the ground station.The station gas management equipment is most efficient if runningconsistently at full utilization rather than spiking in demand. To levelthis, the gases are captured and stored, then passed through the gasmanagement system at a consistent rate and stored for use—eitherselling, chemical operation or power generation. As a roughapproximation, the lowest cost for ground capital is to have the gasesproduced in each platform cycle take the full cycle to process, whichplaces an approximate time scale for the storage of the gas. This can belengthened to provide buffer to the supply chain.

The most energy efficient mode for gas storage is to store the gasnearly at the pressure in which the floating solar energy facilityoutputs them. The hydrogen gas is output at approximately 50-65% of themaximum tank pressure, as the tank is retains some fuel for droneoperation by the floating solar energy facility. The pressure will startat the maximum tank pressure (about 2 MPa in one non-limiting examplemode) and drop to about 50-65% of this (1-1.3 MPa) before the floatingsolar energy facility is ready for heading back out. The stationhydrogen pressure can then be held at about 1-1.3 MPa without requiringany substantial pumping equipment or energy demand. This significantlysimplifies the gas operation, as the floating solar energy facilitysource is providing the pressure. This low pressure is advantageousbecause, below 20 bar, hydrogen can be safely carried in existing steeland plastic pipes. At higher pressures, such as 40 bar and higher, thereis risk of hydrogen being absorbed into the material of the pipe, whichcould cause hydrogen embrittlement in the case of some metals and wouldbe difficult to contain in plastic.

The oxygen gas is output at the maximum tank pressure (2 MPa in theexample mode) and will drop to atmospheric pressure upon fully emptying(0.1 MPa). The oxygen pressure in the station can then be held atapproximately atmospheric pressure.

Given that hydrogen is buoyant, storing it at pressure reduces issues ofbuoyancy on the station equipment, but this is not a problem for oxygen.Thus, while hydrogen is generally held in a compressed or liquefiedmode, the oxygen generated in this system is not nearly as restrictive.It may be stored in flexible containers. It is more dense, less likelyto leak, is of less value (can be replaced cheaply) and not a directexplosion hazard. It is envisioned that the oxygen may be stored inflexible chambers like the balloon for the floating solar energyfacility; this would tap into the manufacturing scale for the floatingsolar energy facility systems, and reduce cost.

The hydrogen storage is best carried out in controlled rigid tanks. Alow cost solution for storage in the station would be to utilize tankssimilar to the ones being mass produced for the floating solar energyfacilities—carbon fiber wrapped tanks with a metal liner. This wouldbenefit from the manufacturing expertise and economies of scale alreadyexploited for other systems. These tanks are the scale of 1-3 m diameterand about 50 kg, so easily movable with conventional equipment. Anoverhead gantry crane may also be used for automated tankremoval/replacement to speed the process. Additionally, many smallertanks provide the opportunity for a more robust storage system, which isa similar approach to the overall use of floating solar energy facilityschools.

One possible station design would be to have the tanks removablyattached to a main horizontal line, with the tanks sitting in pits dugin the ground (or in concrete), so the tank is fully below ground level.The tanks could also be placed in concrete cells above ground. The topof the pit would be covered by an air-permeable grating, but that wouldkeep objects from falling onto the tank. The pits provide a low costsafety mechanism to contain gas losses or explosions and to keep thetanks decoupled. The top grating may be removed and the tanks lifted outof the pit for maintenance or inspection. Hydrogen sensors in each pitcan be used to indicate when a tank requires special inspection. Bymaking the tanks removable from the main line, maintenance may becarried out without interrupting the full scale operation. A new tankwould be switched in, and the old tank moved to an inspection facility.The pit provides further safety as it could easily be flooded with aprotection agent such as heavy inert gas, carbon dioxide, water, orfire-retardant foam in the case of fire or emergency. This would sealoff the tanks from one another and from oxygen, halting any spread ofdamage.

Failure Issues

In the case of a floating solar energy facility crash into the rails,the ground capture vehicles could push the wreckage down the rail awayfrom the working area. Other sections of the rail could also be used byrerouting the floating solar energy facilities around the bays, perhapsthrough various ground capture vehicle regions.

Mobile Stations

The station setup may be put onto a ship for polar operation, andreduced in scale by several steps. A main line would be set up down thecenter of the airborne floating solar energy facility, with groundcapture vehicles on either side. The ships are generally about 70 mwide, and 300-400 m long, meaning they can have about 20× ground capturevehicles per main line. It may be possible to stack several lines andground capture vehicle systems, perhaps up to 3×, providing the shipwith approximately 1 GW worth of capability. Stations may also bedeployed in floating boats around the main tanker to expand thecapability.

Emergency Power Demand

The floating solar energy facilities each carry a substantial amount ofhydrogen used for buoyancy, about 5-10× a single cycle. In the case ofan emergency power demand, this lift gas can be extracted from thefloating solar energy facilities to provide a burst of fuel. Normalcyclic operation would only transfer out the hydrogen generated ataltitude from water electrolysis; it would not extract the lift gas forpower. However if the energy is needed it can be made available. Theexchange is that the floating solar energy facilities can no longer takeoff afterwards. They must instead be grounded until enough hydrogen isgenerated to provide full lift control.

Grounded floating solar energy facility platforms can also be used asgrid storage, as they can be plugged into DC from the grid (through aninverter) and their electrolysis systems used to convert excess gridpower to stored hydrogen, which can be processed with the existinginfrastructure. This may be done during the night with floating solarenergy facilities that are to be released at daylight. Alternatively,the storage can be done with electrolysis units that are removed fromthe floating solar energy facility.

Safety Mechanisms

There are several main scenarios that need to be accounted for regardingthe safety of the solar energy facility: 1) the floating solar energyfacility loses lift, 2) the floating solar energy facility is hit byanother air vehicle, and 3) the floating solar energy facility misses onlanding.

There are many safety mechanisms employed on the platform in order toprevent danger to mitigate the risk from each of the scenarios laid outabove. The ultimate goal here is to ensure that there is never anuncontrolled landing of energetic chemicals.

The safety mechanisms can broadly be separated into four main levels asnoted below: i) intra-platform, ii) inter-platform, iii) shepherd ships,and iv) ground based.

Shepherd System

A Shepherd ship is also a lighter-than-air Unmanned Aerial Systems(UAS), with the role of acting as a secondary safety net should theprimary capture mechanisms fail. These Shepherd ships may be standardfloating solar energy facilities operating below the school, or may bespecialized systems with extra communications and imaging equipment toenable ground based controllers to communicate with the floating solarenergy facilities even in poor conditions. The presently non-limitingexample mode is to use the standard floating solar energy facility, asit is mass-produced, and is able to run through the standard cycleincluding cyclic ground inspection without any requirements overstandard floating solar energy facilities. The Shepherd ship would belocated below the school. When a floating solar energy facility beginsto fail or show issues related to operational problems, the Shepherdship would immediately proceed to place itself nearly below the damagedsystem. It could use the standard onboard drone to attach to the damagedfloating solar energy facility if needed, and would vent unusedprecursor chemical (water) if extra buoyancy is needed to hold thedamaged system. As soon as the Shepherd ship is occupied with thedamaged system, another floating solar energy facility from the flockwould be designated to fill the guard spot formerly held by the occupiedShepherd ship, and shifted into the station below the flock. Thisguarantees there is always a secondary safety net.

Shepherd ships are deployed with a “school” (group) of solar energyfacilities to provide sensing and backup for emergencies. For example,when a solar energy facility finds itself in an uncontrolled loss ofaltitude, the Shepherd ship can image and potentially guide the floatingsolar energy facility down.

The Shepherd ships may also have deployable fast UASs that can get todamaged floating solar energy facilities for imaging, or controlpurposes. These deployable UASs may also be provided to a subset of thestandard floating solar energy facilities. The deployable UASs may befast moving vehicles such as fixed wing craft, which can rapidlymaneuver over to the damaged vehicle to get an image, and possibleestablish a connection to the damaged system. Such a connection may beused, for example, to physically connect the damaged system to a healthyfloating solar energy facility via a tether carried by the UAS, or theUAS may attach and deploy a small parachute that slows the descent ofthe floating solar energy facility. The combination of floating solarenergy facility plus parachute may then be used to guide the floatingsolar energy facility to a controlled landing.

Shepherd ships may also have sensing to detect incoming objects such asplanes. They can radio to the plane to warn of the school as well assend signals to the school or errant solar energy facility to eithergain or drop altitude to avoid a collision or to cut the tank loose, asa last resort, should it look like a collision is inevitable.

Priority of Safety Mechanisms

The four main levels of the safety mechanisms, i) intra-platform, ii)inter-platform, iii) Shepherd ships, and iv) ground based, are orderedby priority of use. The priority of use is dependent on a measure ofnearness to the issue and thus rapidity of response. The first levelincludes safety mechanisms on each floating solar energy facilityplatform for use on itself. These all have the critical flaw that theycan fail and can be taken out en masse by certain events such as anonboard explosion. The second level of safety, inter-platform, isengaged when the first level fails. This level utilizes the nearbyfloating solar energy facility platforms as sources of information andcontrol over the damaged floating solar energy facility. The use ofmultiple independent systems provides significant redundancy, howeverthese systems may not be able to reach the damaged system in time. Thethird level employs Shepherd ships, which are described infra. Shepherdships may be utilized when the inter-platform level is insufficient,such as in cases of rapid failures. The Shepherd ships are located justbelow the main grouping within the school of floating solar energyfacilities, to act as backup. The fourth level of ground-basedinterception is utilized when the third level is insufficient, andrelies on UAVs sourced from the ground to act as the final layer(s) ofredundancy to observe, track and control the descent of the damagedsystem.

Intra-Platform

-   -   Self-healing balloon    -   Fire retardant process    -   Hydrogen vents on balloon    -   Multiple layers to lift gas balloon    -   Air exchange via air compressors    -   Passive buoyancy of the floating solar energy facility    -   Backup hydrogen for excess lift    -   Altitude triggering dead-man switches to vent oxygen and        hydrogen    -   Acceleration triggering dead-man switches to trigger        balloon/tank separation    -   Paragliding wings for controlled descent    -   Separable balloon/tank with parachute on the balloon    -   Lights to warn off vehicles    -   Radar reflective balloon skin    -   Operation above plane airspace    -   Operation over generally uninhabited areas    -   Operation through air corridors    -   Cyclic equipment monitoring

Inter-Platform

-   -   School based observation and control

Shepherd Ships

-   -   Shepherd ship observation and control

Ground-Based

-   -   Active local radar to warn system when planes are approaching    -   Ground-based interception

Fire and Leak Resistance

The fire and leak scenario includes cases in which the balloon isleaking gas and and/or the gas has lit on fire. This must either behalted or the prevented from accelerating, preferably both. The “burningballoon” scenario has been studied for small drones, and is known tocause a flame when the balloon fabric is inelastic, rather than anexplosion. The Mylar film is not elastic, nor does it catastrophicallyfail, so the hydrogen only meets oxygen at a small point. There islittle overpressure, so the gas jet is not large. The polymer in theMylar is not significantly flammable, so the fire spreads, but not withextreme speed.

First, the flames can be slowed by including fire retardant agents inthe balloon fabric. Second, at altitude there is little oxygen to supplythe flames, so by overdriving the air pressure side it may be possibleto blow out the flame, reducing the fraction of oxidizer below ignitionlevels. A possible pressure overdrive would involve venting hydrogenrapidly as well as pressurizing the air side; this may raise theinternal pressure sufficiently to blow out the flame. Third, a smallsupply of fire retardant and/or hole patching material may be storedinside the hydrogen balloon side, and be directed by a small turret andcamera type setup. This might be searching for light and heat, and willthen spray an expanding foam hole sealing agent at the bright spot toact as both a patch and to break the supply of fuel to the flame (ifany). The hole patching material may be anything from a quick-dryexpanding foam to confetti-like material with tacky surface coatings.Fourth, flaps of excess material can be left hanging in the interior ofthe balloon, to be drawn via air currents to the source of a leak, andact as temporary plugs. Fifth, surface monitoring drones may be used toexplore for leaks and attempt to plug them, by sensing leaks with airflow and hydrogen sensors. These may be located both on the inside andoutside surface. One example of this would be robots with three or moresuction-cup feet, where air is blown in through a circumferential ringand vacuum is drawn through a hole in the center of the foot. By blowingair through the ring while drawing vacuum, the robot may skate along thesurface without direct contact. The use of a fourth foot would allow thedrone to step over obstacles without losing three-point contact. Smallturbofans would allow the robot to propel along the surface, whilelooking at the balloon skin. When a leak or tear area is found, therobot may install a patch over the hole by turning off the air flow andonly drawing vacuum. This would anchor it down to the surface, so it mayperform delicate repairs and/or patching work.

An envisioned possible setup for the low-altitude, smaller floatingsolar energy facilities, would be to have the hydrogen chamber fullyenclosed by the air chamber, with both chambers having excess materialflaps for passive plugging, and the hydrogen chamber having an activelycontrollable fire retardant/hole patching small turret. For thehigh-altitude version, flaps of material may be hung down in bothchambers to act as passive blocks for leaks, and a fireretardant/hole-patch turret may be placed within the hydrogen chamber,with a leak patching robot on the outer surface, powered from either thehydrogen or the PV solar panels.

Loss of Lift

There could be many reasons the floating solar energy facility mayuncontrollably lose lift and the computer cannot regain control. In thisscenario the system first has actively noted that it is losing altitude.The generation of hydrogen provides an additional source to temporarilymaintain lift if the leak is small. The system will evaluate if the leakrate will allow for the floating solar energy facility to continue onthe normal cycle and simply note this for maintenance upon return. Ifthe leak is too rapid, or if the leak rate of change (when extrapolated)would lead to rapid gas loss, then the emergency controlled landingprocess is engaged. The helpful feature of passive buoyancy is thatfailures are not instantaneously critical. This provides time to employthe multiple levels of safety systems.

The system will first vent the water or other non-essential mass fromthe tank in order to reduce load, then vent oxygen. In the case of theburning floating solar energy facility situation, the oxygen would bevented away from the floating solar energy facility. The hydrogen isvented just before contact with the ground (say 1-2 km up), as it isvaluable for retaining buoyancy and reducing the fall rate until theend. Dead-man switches would provide a failsafe to ensure the ventingoccurs before landing, even if power is lost. The air pump will continueto try to inflate the balloon, largely maintaining the shape and slowingthe terminal velocity of the fall.

A second floating solar energy facility would be tasked to monitor theone coming down for emergency landing, and travel with it. The secondfloating solar energy facility can, by way of non-limiting examples, beeither another floating solar energy facility platform or a Shepherdship. This tasking occurs the moment the floating solar energy facilityswitches to emergency controlled landing state or goes offline.Controllers are used to drive the platform to a controlled landing in anunpopulated area, which may be back at the station. If the damagedfloating solar energy facility is able to carry out a controlledlanding, then the Shepherd ship is used to observe the process and thelanding spot, and then return to the school.

If the damaged floating solar energy facility's condition worsens andthe system notes that it is not able to come down in a controlleddescent (defined as having the ability to control the landing speed tobelow a threshold and control the landing location), or if the secondfloating solar energy facility starts to lose the ability to maintainclose proximity to the damaged platform, then the damaged platform isshifted into uncontrolled descent mode. The uncontrolled descent modemay be immediately initiated. By way of non-limiting example, threelayers of safety are provided, which are: i) inter-platform, ii)Shepherd ship, and iii) ground based. All three of these sources candeploy fast UAVs such as quadcopters or fixed wing craft which canquickly reach the damaged platform. The present non-limiting examplemode is a fixed wing craft, which could be operated vertically to holdposition like a helicopter. The fixed wing craft offer more rapid flightto and from the damaged floating solar energy facility. These fast UAVscan image the damaged system, and provide information for thecontrollers on how to solve it. They can also interact with the platformto try and control its descent by a number of means including: i)attaching a tether to it that connects to another platform, ii)attaching a small parachute that can slow descent, iii) attaching theUAV to the damaged platform to begin steering it. The attachment can bemade via clips to hard mounting points or a deployed net, or any otherconvenient technique. When its use is complete, the fast UAV would flyback to its floating solar energy facility platform, close to its launchspot, and can be reeled in via the tether connecting it to the mainplatform. It is envisioned that the entire fast UAV may be used as ananchor to get tangled in the other floating solar energy facilities'lines, and may have barb like attachments on its wings to ensure linesare captured. Alternatively, it may have an arm that could be flippedout with the tether and hook at the end. The imaging system on the fastUAV would be able to see the extended arm, and the fast UAV would fly bythe damaged system, close enough for the arm to drag along the surfaceand clip the hook on a line or hardpoint anchoring spot as would belocated all on the main platform.

Only a fraction of the platforms will likely carry these fast-UAVs asthey will reduce energy capture efficiency. These would be the smallestsystems and would likely use a tether. If the inter-platform controlfails, the Shepherd systems can deploy fast UAVs. If all of these fail,the ground station can deploy fast UAVs to ascend up to meet theuncontrolled damaged platform. It is expected that the damaged platformwould be limited in its terminal velocity by the large size andrelatively low mass, meaning there may be anywhere up to a half hour toengage the uncontrolled descent.

Ground-based systems may, by way of non-limiting example, deploy nets orhooks to capture falling components and bring them back to the station.These fast-UAVs are sent off from ground when any issue arises, and haveboth imaging systems as well as the ability to clip to a floating solarenergy facility platform, and possibly attach a releasable drogue chuteto the platform. An envisioned setup for this is a fixed wing dronewhich can hover by orienting itself vertically. The fast-UAV would havean imaging system and a fold-out arm below it which would have a hookattached to a drogue parachute. The fast UAV may i) attach the hook andmaintain contact with the damaged drone and try to use itswings/thrusters to control the object, ii) leave behind the attacheddrogue parachute, and deploy the parachute by flying away from it, as aline would connect the parachute to the fast-UAV. The line connectingthe deployed parachute to the fast-UAV may be used to steer the nowslower object, or the fast-UAV may also release that to let the objectreturn on its own. The ground-based systems can be massively redundant,so dozens of fast UAVs may be deployed to make attempts at captureduring the full length of the descent. Multiple quadcopters could deploya net to capture tumbling parts, for example.

If no other platform is able to gain control of the damaged floatingsolar energy facility while in uncontrolled descent, a “release” commandmay be given. In response to the “release command”, the balloon can becut from the tank, and the parachute unfurled, leaving the tank withfunctional paragliding wings to make a controlled (by a pilot) landing.This offers the possibility to reduce the rate of descent and clear awaydamaged components if the balloon is fouling the parachute. This may beset to occur automatically by a dead-man switch (independently powered)if the descent velocity is above a threshold (say the balloon is torn topieces and is obstructing the parachute deployment). Normally, the“release” command would be overridden by the active controller, and ifthe floating solar energy facility is under controlled descent it wouldnot be at a velocity sufficient to trigger the “release” command.Likewise, the venting of the stored chemicals (water, oxygen andhydrogen in the example mode) will all be set to occur by altitude-baseddead-man switches that must be overridden upon descent. Thus, regardlessof whether the damaged floating solar energy facility reaches anuncontrolled descent stage by power loss, or catastrophic damage, it isassured to be an empty tank slowly parachuting to the ground by the timeit reaches ground. In all situations the wings and balloon will limitdescent speed and have some maneuverability to control landing rate andlocation.

The above renders four possible outcomes:

1) a controlled descent with no fuel,

2) a controlled descent with full fuel,

3) an uncontrolled descent with no fuel, and

4) an uncontrolled descent with full fuel.

The major focus in this scenario is driving the outcome towards thelower numbers, ensuring a controlled descent, as this makes it possibleto find a safe landing space and thus remove the risk to the populationbelow. The only route to a fuel-filled uncontrolled descent is throughi) a failure of power before the emergency process kicked in, ii) afailure of all dead-man intra-platform safety measures, iii) a failureof the UAVs assigned to floating solar energy facilities to control thefloating solar energy facilities, iv) a failure of the Shepherd ship tocontrol the platform, and v) a failure of the ground-based interception.

The main problem is a combination of a major leak and power loss. Thiswould cause rapid descent with no control, possibly before Shepherdships could reach the damaged floating solar energy facility. A possiblemethod for such a sudden change is an explosion onboard, which has thebenefit of likely emptying the system of the fuel and hopefullydispersing the tank into numerous small parts which have low terminalvelocity. If the explosion does not immediately result in the systemfalling out of the sky, for example, as the result of only a minor leakplus power loss, then the Shepherd ship can control the landing(outcome 1) or the system will passively slowly sink to the ground viaballoon and/or parachute (outcome 3), and can be controlled via theinter-platform, Shepherd ship or ground-based safety mechanisms.

To mitigate the risk of outcomes 3 and 4, the large schools of floatingsolar energy facilities would generally be over low to zero populationareas, for instance over the ocean. The controlled landing would likelybe back at the power station, given that the school would generally setup in a grid directly above the power station.

Air Vehicle Conflicts

There are several safety measures deployed on the solar energy facilityto attempt to avoid collisions with airplanes. The first is that thesolar energy facility should always be at an altitude above commercialflights during harvesting and should only be ascending/descending in theprescribed airspace, under active control. This is ensured by the use ofthe guide balloon during any power loss, so at least one active,controlled system is available. An active floating solar energy facilitywill broadcast its position, which can be detected by TCAS (secondarysurveillance radar, if a transponder is used for the broadcast), so airtraffic can be rerouted should it leave its assigned airspace. It willalso be able to control that position to miss incoming planes if theimminent collision is noted with sufficient time. The threshold forsufficient time would likely be 10's of km separation. A monitoredsection of airspace around the floating solar energy facilities wouldprovide the buffer of scale 10 km to give the systems sufficient time toreact. The emergency measures would be engaged should the floating solarenergy facility or pair stray outside its assigned airspace, or intoprescribed air corridors, and air traffic notices an incoming plane on acollision course. The second measure is that the solar energy facilityhas an inherently large radar signature from the aluminized skin of theballoon and tank so that it will easily appear as a primary ATC radartarget, as well as having lights. This should help warn planes of thesolar energy facility by radar. Third, the base of operations from whichthe floating solar energy facility cyclically travels may have a TCASradar tracking device, or other sensor station so as to determine thelocation of both the UAV platforms as well as other aircraft. This couldbe used to avoid possible collisions by heading off the aircraft orchanging the platforms' trajectories. Since the platforms are generallyjust traveling up a vertical air column to the operating altitude, thendeploying and holding position, this may all easily be covered by thebase station radar. Finally, in the case of an impending collision,sensed by a local sensor network on the floating solar energy facilitiesfor high speed incoming objects, the balloon and tank can be detached,separating so as to let the air vehicle fly through unobstructed.

Missed Approach

Should there be problems on landing, the platform has the option ofusing thrusters to attempt to circle around or to regain lift and comearound for another landing in a few minutes. Once the solar energyfacility has gained enough altitude it can attempt to descend again,using the wings and thrusters to guide it back on course.

Should be solar energy facility be unable to regain altitude or in anyother way be uncontrolled, say under high winds, the ground station willhave emergency catchers (either human or UAV), which are the fourth tierof safety-ground-based interception UAVs. These would attempt to hookthe solar energy facility to help bring it in. In addition, the groundstation is equipped with nets and a safety zone around the edges tominimize issues with potential crashes. The UAV catcher would be a highspeed drone with a cable and attachment structure (say hook), waitingjust after the end of the landing zone. If the floating solar energyfacility misses, the drone is launched and snags the floating solarenergy facility. Multiple catchers may be placed at the end of thefield, automatically waiting for a floating solar energy facility tocome into their zone and then trying to essentially ram it to hook it.

The catcher drone may be an effective standard method to use for alllandings, where each incoming floating solar energy facility (generallyonly at 20 mph scale) gets a drone guide, holding an attachment hook ona line with the reel on a moving sled. This setup matches speed with thefloating solar energy facility, and the drone anchors the floating solarenergy facility in place. This can be run several times and the dronecan continue to chase the floating solar energy facility for a distanceto provide sufficient hooking chances. A redundant ground capturevehicle and catcher drone may be deployed at midway along the rail incase the main catcher is unsuccessful.

Tether Damage

In this scenario, the main tethers either fray or are cut. To ensurethat the system can still work, there are two backups. First, eachtether may be is doubled, so a broken tether simply passes the load tothe other. Each have very high safety factors for solo operation, sowill be effective alone. Additionally, if both are cut then the verticaltethers alone can hold the balloon and tank together. If one of the maintethers is totally lost and so is the side vertical tether, any one linecan hold up the tank, with the only loss being the controlled use of theparagliding wing. The thrusters can still be used. In the worst case, ifthe tank is dangling and the power to thrusters are cut, the systemstill retains buoyancy so is in no immediate danger. It can shift toemergency return mode, and rely on the Shepherd ship to tow it home.

Variations

Several concepts are suggested for later version designs; this includesadjustments to the design presented above as well as the use ofadditional vehicles in the process.

Shuttle

A larger scale version of the design concept includes the use of aseparate vehicle for transporting the tanks up to altitude and back downagain. This shuttle would take off like a floating solar energyfacility, and could be controlled via two inflatable segments, locatedat the front and back ends of the shuttle. By way of non-limitingexample, the shuttle would have a long cylindrical body with theinflatable balloons at either end, and a symmetric set of large inflatedwings in the center. Also in the center would be a bay for storingmultiple tanks, with doors that could open upwards to access the tanks.By way of non-limiting example, the ends of the wings would have axiallyaligned propellers.

Upon reaching altitude, the shuttle balances the lift between the twoballoons, which allows the shuttle to hold stationary and horizontal ataltitude without drawing power. The shuttle then adjusts its twoballoons for z axis control and use its two propellers for x and θ zcontrol to position itself under an energy harvester. Once below, agantry arm may grab and remove the full tank, then replace it with afull one. This arrangement has the advantage of moving the tanks, ratherthan directly transferring the gas, as the gas would require re-pumping.

The shuttle gathers as many tanks as it could fit, which, in turn,reduces lift in the front balloon and start to tip/glide on down toground. By way of non-limiting example, the shuttle could gather 5-10tanks, although a much larger number, such as 100 or 500 tanks, could begathered. The balloons would be gradually emptied and width drawn intothe shuttle so it may land as a plane. This allows for fine control ofthe landing process as well as a rapid descent.

Such a system would enable rapid controlled transit, while keeping theharvesters where they are most effective—at altitude, and using a planelike vehicle to transit the highly populated airspace. The use ofmultiple tank carrying capacity would reduce the number of traveliterations, reducing the issue with passing through jet accessible airspace. The energy harvesters would simply stay at altitude for longperiods of perhaps a year or more at a time, gathering energy.

The shuttle would also provide easy access to repair/maintenance for theother envisioned system capabilities (imaging, surveillance,telecommunications, etc.) and would serve as a platform for the intendedlow earth orbit access. In this application, it would serve as anedge-of-atmosphere space shuttle.

The shuttle would allow deployment of large scale arrays over populatedareas. Since the floating solar energy facilities would be staying ataltitude, only tightly controlled vehicles would be needed for going upand down.

Floating Solar Energy Facility Coupling

Floating solar energy facilities may be controlled to come into nearcontact at altitude in order to tap into the wind screening effect; thiswould lower the drag on the sequential floating solar energy facilities,reducing the power demand.

Balloon Geometry

A possible improvement of the balloon geometry would involve shiftingthe balloon to a more ellipsoid Y-Z axis cross-section which wouldprovide further area for panels. It may also be possible to use thefloating solar energy facility geometry to generate lift in the steadyheadwinds it will face; this could reduce the required size of thefloating solar energy facility. This may well be possible using theparagliding wings.

Solar Energy Capture

Future designs may find it more effective to use solar thermalelectrolysis, or some sort of a solar to mechanical to electricalprocess to gather more energy. Alternately, lightweight solarconcentrators (such as the inflatable lens concept) would be ideal forreducing the solar panel mass while retaining the same power andgenerally same cost structure. The solar panel mass comprises a majoritylarge portion of the overall mass and so would provide significant gainsin the system if reduced.

Transfer of Energy to an Electrical Grid

The aerosolar energy harvesting system may be used to augment aterrestrial based energy production facility having an interruptibleenergy source, such as a solar or wind energy production facility. Inthat function, the ground station may be located close to theterrestrial based energy production facility as to permit the energytransferred to the ground station to augment the energy of theterrestrial based energy production facility. The terrestrial basedenergy production facility would be able to use the energy transferredby the ground station to provide the ground-based energy productionfacility with an energy supply for use when the ground-based energyproduction facility produces below an allowable grid delivery rate forthe ground-based energy production facility.

By associating the ground station with the terrestrial based energyproduction facility, the interconnection capacity of the ground stationcan be used to transfer energy to an electrical grid when theterrestrial based energy production facility is interrupted or belowcapacity. Such interrupted or below-capacity operation would be the casewith a terrestrial solar energy production facility at night. Thisallows using the landed energy storage system to provide a controllableload to take excess generation from the grid for storage and laterdelivery. The ground station may also be located off shore and providingthe transfer of energy to the grid on shore via a submarine or floatingpower cable system.

Hydrogen Storage

It may be possible to reduce the overall tank cost and mass by storingthe hydrogen in liquid form; however, the process to chill and maintainhydrogen in its liquid form consumes a substantial amount of energy andhardware.

Other Forms of Energy Capture Automated Vehicles

This same concept may be extensible to other vehicles, including boats.Clusters of energy harvesting boats could avoid clouds and storms, andthen produce fresh water from the distillation of the seawater (or usingsolar thermal evaporation to generate pure water).

Storage and Transport

Drone compressed storage could be useful to reducing the area requiredto store the drones when they are brought down, it could also help intransportation. The drones could be compressed for storage, by lettingall of the air out of the air chamber. Several steps could be taken toavoid damaging the drone.

First, the drone skin could be developed to have several locations,folding joints, where the carbon fiber is replaced with a specificallyflexible foldable fiber. Carbon fiber is desired for the fabric due toits mass production scale, high strength to weight and UV resistance;however, it is liable to damage when creased. The use of flexiblefoldable fiber joints would localize the creases and help the structureto bend at only specific locations if needed. Localizing the crease tospecific joint locations would expand the range of materials that couldbe used in the balloon fabric. A possible location for this joint in theskin material would be along the joining line between gores. Thepreferred layout for the gores in the balloon is from front to back, soeach gore stretches nearly the full length of the balloon from furthest+x extent to furthest −x extent.

Second, the enforced bends could be constrained by a low cost clampingelement to limits the minimum radius of curvature, so as to ensure thematerial never reaches a dangerous threshold. This would effectively bea bar that the material is wrapped around, and perhaps a c-shaped crosssection clip that would go around the outside. The combination wouldenforce a certain minimum radius of curvature to the material, but couldbe removed during unpacking.

Third, the main elements on the structure would need to be removed,which may, by non-limiting example be tension lines, tethers, panels,compression elements and thrusters. This would leave only the nestedballoons as a structure.

Fourth, several kinds of folding could be used, one of which isdescribed here. It is desired to bring the overall packed drone balloonvolume down to an easily shippable size, such as that of a shippingcontainer. Fold joints could be placed on the balloon running along thetop and bottom from the front to the back of the design. These pointsmark the edges of the balloon in FIGS. 1A, 1B and 2. Once the front andback end caps (at the poles of the system) are removed, the ballooncould then be laid out roughly flat on the ground without fold damage.Depending on the size, the balloon could be folded along its long axisone more time if desired, which would need either a fold constraint orfold joint. The constraint (foam bar, etc.) would be acceptable here asit could be inserted before the structure is folded, which is notpossible for the top and bottom edge. The fold along the long axisshrinks the extension of the balloon down to generally under 15 m,which, by way of non-limiting example, may be the maximum length of acargo container. Now the drone as a flat sheet could be compressed intoa wave-like meander pattern which expands it into the third dimensionand reduces length. Such at pattern can be rolled back on itself to makemultiple layers. Thus it should be possible to fit the whole structureinto the cargo container such that it unrolls out from the long face.The meander compression could be enabled by using a packing frame withlarge rollers that the structure is wrapped around. This would make thecompression process easy and stable once complete.

In the station, the drone could be compacted by letting the air out, andletting the drone fold along its spinal fold material running along thetop and bottom. The solar panel array would need to have a gap in it toallow it to fold to either side of the top spine. The drone would haveto be hung or supported by a frame to ensure the thrusters and otheritems do not damage the skin. This should reduce the width by asignificant factor, almost 10×, once the air is removed.

Balloon Fabrication

A possible means of mass production of the balloon skin is suggested bythe folding joints concept. This would be to form gores of the desiredlaminate with high performance biaxially oriented carbon fiber. Thegores would extend from the front to back of the balloon (+x to −xdirection extent). Such gores could be mass manufactured as a flatlaminate and with both axes of fiber laid down, perhaps one aligned tothe long axis of the gore and one perpendicular to it. The fiber wouldextend out to just before the edges of the gore.

The non-fiber covered edges of the gore would be heat sealed to the nextgore over, and a tape composed of the foldable joint fiber would beplaced down over this seam. Thus every joint between every gore couldbecome a foldable joint, and the whole structure could be packed up ifneeded without creasing the carbon fiber. Such design decoupling wouldprovide the benefits of both material and flexibility, as the majorityof the surface area of the balloon would thus be the highstrength-to-weight carbon fiber, but it would have a level offoldability that could not be found by a fully carbon fiber structureand is usually associated with much more expensive/heavier materials.

CONCLUSION

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed and illustrated to explain the nature of the subject matter,may be made by those skilled in the art within the principle and scopeof the invention as expressed in the appended claims.

What is claimed is:
 1. An airborne energy collection vehicle comprising:a balloon structure comprising a lighter than air envelope structurecomprising: an outer gas envelope formed of a substantially inelasticmaterial; at least one inner gas envelope at least partially separatefrom the outer gas envelope, contained within the outer gas envelope,and configured to hold lifting gas as a buoyancy medium for the airborneenergy collection vehicle, with at least a portion of a space betweenthe inner gas envelope and outer gas envelope filled with air; aflexible diaphragm forming at least a portion of the inner gas envelopeseparate from the outer gas envelope and contained within the outer gasenvelope, whereby the flexible diaphragm causes the inner gas envelopeto maintain an equilibrium pressure with the outer gas envelope andallows expansion and contraction of the inner gas envelope tosubstantially fill the space of the outer gas envelope from a relativelysmaller fraction of the outer gas envelope; an air chamberpressurization mechanism capable of maintaining the outer gas envelopegas pressure at a target value; an air chamber pressurization controllerthat monitors the outer gas envelope pressure and either pumps in air orvents air to bring a gauge pressure to the target value; a photovoltaiccollector array receiving solar energy; an energy storage facilityreceiving energy from the photovoltaic collector array and convertingthe energy to stored energy.
 2. The airborne energy collection vehicleof claim 1, further comprising: a lifting gas storage container arraycomprising at least one lifting gas storage tank; a fuel precursorsupply; the energy conversion plant using the received energy from thephotovoltaic collector array to convert precursor material from theprecursor supply to a high energy fuel as the stored energy.
 3. Theairborne energy collection vehicle of claim 1, wherein: the fuelprecursor comprises water, and wherein the lifting gas and the highenergy fuel comprise hydrogen, and wherein said one lifting gas storagetank provides storage for the hydrogen produced by the energy conversionplant.
 4. The airborne energy collection vehicle of claim 1, wherein:the energy storage facility comprises storage batteries.
 5. The airborneenergy collection vehicle of claim 1, wherein: the energy storagefacility comprises an inertial mass.
 6. The airborne energy collectionvehicle of claim 1, wherein: the outer gas envelope substantiallycontains the inner gas envelope, thereby providing structural integrityand puncture resistance to the inner gas envelope to allow foroptimization of leakage characteristics of the inner gas envelope aspart of a puncture resistant lighter than air envelope structure.
 7. Theairborne energy collection vehicle of claim 1, further comprising: gassupply controllers separately controlling gas supply to the outer gasenvelope and lifting gas supply to the inner gas envelope, therebymaintaining a safe and controlled inflation pressure and providing aconsistently inflated body structure; and at least one thruster mountedto the body structure.
 8. The airborne energy collection vehicle ofclaim 1, further comprising: a plurality of tethers connecting theballoon structure to an externally carried section, the externallycarried section carrying the lifting gas storage container array, theprecursor supply and the energy conversion plant; and the plurality oftethers having a configuration for shifting a position of the outer gasenvelope to facilitate navigation and to position the photovoltaiccollector array to an optimum position for receiving solar energy inaccordance with the incidence of solar energy on the airborne energycollection vehicle.
 9. The airborne energy collection vehicle of claim1, further comprising: the photovoltaic collector array mounted at aposition away from a top position of the outer gas envelope sufficientto permit the airborne energy collection vehicle to position thephotovoltaic collector array in an optimal position with respect to thesun by tilting and rotation of the airborne energy collection vehicle.10. The airborne energy collection vehicle of claim 9, wherein themounting of the photovoltaic collector array centers the photovoltaiccollector array at close to 45° from a top position in a manner toconfigure the airborne energy collection vehicle to achieve the optimalposition with respect to the sun with a minimized range of tilting ofthe airborne energy collection vehicle.
 11. The airborne energycollection vehicle of claim 1, further comprising: a transfer mechanismcomprising a pump for transferring lifting gas between the inner gasenvelope and the lifting gas storage container;
 12. The airborne energycollection vehicle of claim 1, further comprising: means for the liftgas to be added to the lift gas envelope from the lifting gas storagetank; and means for the lift gas to be transferred by at least one ofventing from the lift gas envelope to the environment or pumped backinto the lifting gas storage tank.
 13. An airborne energy collectionsystem comprising: a plurality of airborne energy collection vehicles,at least a subset of the airborne energy collection vehicles eachcomprising: a lighter than air envelope structure comprising: an outergas envelope; an inner gas envelope at least partially separate from theouter gas envelope, contained within the outer gas envelope, andconfigured to hold lifting gas as a buoyancy medium for the airborneenergy collection vehicle, with at least a portion of a space betweenthe inner gas envelope and outer gas envelope filled with air; aflexible diaphragm forming at least a portion of the inner gas envelopeseparate from the outer gas envelope and contained within the outer gasenvelope, whereby the flexible diaphragm causes the inner gas envelopeto maintain an equilibrium pressure with the outer gas envelope; anenergy production unit comprising a photovoltaic collector arrayreceiving solar energy; an energy conversion unit receiving energy fromthe photovoltaic collector array and converting the energy for storage;at least one airborne vehicle providing a docking port for a drone,wherein the drone provides a capability of monitoring, maintenance,repair or rescue of the plurality of airborne rescue vehicles includingconfiguring a damaged airborne energy collection vehicle for recovery.14. The airborne energy collection system of claim 13, wherein theconfiguring the damaged airborne energy collection vehicle for recoverycomprises, in the case of a determination that one airborne energycollection vehicle can link to a damaged airborne energy collectionvehicle without damaging said one airborne energy collection vehicle,the drone links said one airborne energy collection vehicle to thedamaged airborne energy collection vehicle.
 15. The airborne energycollection system of claim 13, wherein the energy conversion unit, uponreceiving energy from the photovoltaic collector array, converts aprecursor material to a high energy fuel.
 16. The airborne energycollection system of claim 13, wherein the energy conversion unit, uponreceiving energy from the photovoltaic collector array, stores thereceived energy as a battery charge.
 17. The airborne energy collectionsystem of claim 13, wherein: the energy conversion unit stores thereceived energy in an energy storage system comprising an inertial mass.18. An airborne energy collection system comprising: a plurality ofairborne energy collection vehicles, at least a subset of the airborneenergy collection vehicles each comprising: a lighter than air envelopestructure comprising: an outer gas envelope; an inner gas envelope atleast partially separate from the outer gas envelope, contained withinthe outer gas envelope, and configured to hold lifting gas as a buoyancymedium for the airborne energy collection vehicle, with at least aportion of a space between the inner gas envelope and outer gas envelopefilled with air; a flexible diaphragm forming at least a portion of theinner gas envelope separate from the outer gas envelope and containedwithin the outer gas envelope, whereby the flexible diaphragm causes theinner gas envelope to maintain an equilibrium pressure with the outergas envelope; an energy production unit comprising a photovoltaiccollector array receiving solar energy; an energy conversion plantreceiving energy from the photovoltaic collector array and convertingthe energy for storage; a ground-based docking system, at a land or sealocation, for transferring energy collected by the airborne energycollection vehicles; an intertie to transfer at least a portion of thetransferred energy to an electrical grid.
 19. The airborne energycollection system of claim 18, further comprising: the ground-baseddocking system located sufficiently close a ground-based energyproduction facility that an interconnection capacity between the dockingsystem and the ground-based energy production facility provides theground-based energy production facility with an energy supply for usewhen the ground-based energy production facility produces below anallowable grid delivery rate for the ground-based energy productionfacility.
 20. The airborne energy collection system of claim 19, furthercomprising: the ground-based energy production facility using thetransferred energy as a part of a landed energy storage system toprovide a controllable load to take excess generation from theelectrical grid for storage and later delivery.
 21. The airborne energycollection system of claim 19, further comprising: the ground-basedenergy production facility located off shore and providing the transferof energy to the grid on shore via a submarine or floating power cablesystem.
 22. The airborne energy collection system of claim 18, furthercomprising: the ground-based docking system located sufficiently close aground-based energy production facility that an interconnection capacityprovides the ground-based solar energy production facility with anenergy supply for use when the ground-based solar energy productionfacility produces below an allowable grid delivery rate for theground-based solar energy production facility.